=Paper= {{Paper |id=Vol-2648/paper24 |storemode=property |title=Combined Neural Network Model for Diagnosing Computer Incidents |pdfUrl=https://ceur-ws.org/Vol-2648/paper24.pdf |volume=Vol-2648 |authors=Vladimir Avramenko,Igor Kotenko,Albert Malikov,Igor Saenko }} ==Combined Neural Network Model for Diagnosing Computer Incidents== https://ceur-ws.org/Vol-2648/paper24.pdf
Combined Neural Network Model for Diagnosing
Computer Incidents
Vladimir Avramenkoa , Igor Kotenkob , Albert Malikova and Igor Saenkob
a
 Military Communication Academy, Saint-Petersburg, Russia
a
 Saint-Petersburg Institute for Information and Automation of the Russian Academy of Sciences, Saint-Petersburg,
Russia


                                         Abstract
                                         The basis for making a decision on responding to computer incidents is information about characteristics
                                         of the identified security breach, the values of which are determined during the diagnosis procedure.
                                         To reduce the time spent on determining the values of characteristics and increase the reliability of the
                                         diagnosis results, it is proposed to use machine learning methods implemented on the basis of artificial
                                         neural networks. The paper considers a combined artificial neural network as the basis of a model for
                                         diagnosing computer incidents. In this model, through the use of deep learning, the drawback of the
                                         classical multilayer perceptron associated with the need to form a massive base of training examples for
                                         the specific structure of the neural network is eliminated. The results of the experiments showed that
                                         the proposed model allows one to reduce the duration of training, while not reducing the values of the
                                         quality indicators of the functioning of the neural network.




1. Introduction
Existing methods for protecting information from unauthorized influences in information and
communication systems suggests a whole arsenal of information protection tools. The im-
provement of information protection technologies is primarily aimed at the early detection of
masked and unknown scenarios for the implementation of security breaches. After detecting a
computer incident, an analysis of the available information is carried out to identify the goals,
causes, possible consequences and other characteristics of a security breach. Based on the anal-
ysis, response measures are taken. At the same time, standard means of information protection
do not allow directly answering key questions of the analysis stage. For this, it is necessary to
collect data from almost all the basic elements of the information and communication system
and characterize the violation that has occurred, i.e. carry out a procedure of diagnosis. It
should be noted that, despite the need to cover the maximum amount of information neces-
sary for making a decision, diagnosis is required to be carried out in the shortest possible time.
Prompt and accurate diagnosis allows one to provide a high security and thereby the steadiness

Russian Advances in Artificial Intelligence: selected contributions to the Russian Conference on Artificial intelligence
(RCAI 2020), October 10-16, 2020, Moscow, Russia
" vsavr@yandex.ru (V. Avramenko); ivkote@comsec.spb.ru (I. Kotenko); mkv.vas@yandex.ru (A. Malikov);
ibsaen@comsec.spb.ru (I. Saenko)

                                       Β© 2020 Copyright for this paper by its authors.
                                       Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
    CEUR
    Workshop
    Proceedings
                  http://ceur-ws.org
                  ISSN 1613-0073       CEUR Workshop Proceedings (CEUR-WS.org)
of information and communication systems. Thus, the diagnosis of computer incidents is an
important stage in managing information protection.
   The need to use a variety of information protection tools in the information security system
entails the complexity of management processes. Continuous improvement of methods for
implementing security breaches and hiding information β€œtraces” requires the use of diagnostic
tools, not limited to a set of predefined rules and template, but taking into account the dy-
namics of events in the information and communication system, resistant to the appearance of
external noises and that operate in close to real time. Existing diagnosis methods consisting in
studying the contents of information sources (reports of protection tools, event logs of servers
and workstations, communication equipment) take a lot of time, and the accuracy of the result
depends on the knowledge and experience of specialists involved. There is a contradiction be-
tween the existing approach to diagnosing computer incidents and modern requirements for
this process.
   This paper proposes a model for diagnosing computer incidents based on a combined neural
network, which is an extension of the approach proposed in the paper [1]. In the process
of functioning of the protection system, new training examples for the diagnostic subsystem
appear; accordingly, correction of combined artificial neural networks is required. Learning
with new examples should be carried out in the shortest possible time. In order to determine
the optimal structure of the neural network, computational experiments were conducted.
   The main theoretical contribution of this work is the formulation and solution of a new
problem of diagnosing computer incidents based on an optimized combined neural network
that provides minimal training time for given requirements for the quality indicators of the
neural network.
   The paper has the following structure. Section 2 provides an overview of relevant work.
Section 3 defines the statement of the problem of diagnosis computer incidents. Sections 4 and
5 consider a combined neural network model for diagnosis computer incidents. Section 6 dis-
cusses the experimental results. Conclusions and directions for further research are presented
in Section 7.


2. Related work
To carry out the procedure for diagnosing computer incidents, it is necessary to organize ef-
fective processing of data from various sources. In works [2, 3, 4, 5], methods of searching,
collecting and processing events occurring in the information system, the appearance of which
is associated with computer incidents, are presented. It is emphasized that it becomes possi-
ble to cope with the analysis of steadily increasing volumes of service information reflected
in audit logs only by organizing effective procedures for automating the processing of event
logs. Traditional approaches for manual investigation of event logs by a security administrator
(without specialized automation tools) are currently extremely inefficient.
   A promising way is the automation of routine diagnosis functions. The procedure for col-
lecting data for diagnosis has been automated for a long time and is represented by various
solutions [6, 7, 8]. And with the procedure for analyzing the collected data, difficulties arise
associated with the high dynamics of the fixed actions of users and events of the information
system, the uncertainty of the relationships between events. Moreover, the analysis is carried
out against a rather pronounced noisy background formed by events that are not related to a
security breach. In order to fulfill the requirements to diagnosis, it is advisable to shift the func-
tions of studying event logs to the "shoulders" of computers. Given the existing experience of
diagnosis, this problem can be solved using one of the methods of machine learning supervised
learning. Training is carried out by finding patterns in the existing already solved examples
of diagnosis, when there is a set of source data and the corresponding correct answer. To im-
plement this method in the tasks of determining categorical output values, machine learning
algorithms based on decision trees and artificial neural networks are most widely used. How-
ever, the use of decision trees in the problem of diagnosing computer incidents is limited due
to the difficulty of adjusting the separating parameters, which can lead to conflicting answers.
Artificial neural networks (namely, multilayer direct distribution neural networks) are more
preferable from this point of view. However, the quality of the classification result is affected
by the dependence of the structure of an artificial neural network on the number of available
training examples. At the same time, the dimension of the input and output layers are deter-
mined by the conditions of the problem being solved, and the dimension of the hidden layer
is selected taking into account the maximization of the quality index of the artificial neural
network.
   It should be noted that the dimension of the input data set (to cover the events that occurred
in a typical information and communication system and affect the outcome of the diagnosis)
is quite large and may amount to several tens of thousands. Learning such a neural network
requires a large amount of training examples. In this regard, it is necessary to carry out op-
timization of the structure of the neural network in order to prevent the negative effect of
retraining the network on a limited number of examples. To this end, it is proposed to build
a combined neural network consisting of the coding part of an auto-encoder and a multilayer
perceptron [1]. Passing through the encoding part of the auto-encoder, the input data is con-
verted into group diagnostic signs of a much smaller dimension. Next, the classification of the
obtained set of group diagnostic features is carried out on the set of values of one characteristic
of a security violation.
   This combined neural network allows you to use a well-known and proven approach to
solving classification problems for a new subject area, in the analysis of computer incidents.
   The use of combined neural networks in the control system of an information security sys-
tem allows one to: (a) provide systematic information for making decisions on responding to
computer incidents; (b) significantly accelerate the processing and analysis of incoming infor-
mation; (c) increase the accuracy of the determined values of information security violation
characteristics; (d) identify the prerequisites for computer incidents. In general, the use of
combined neural networks in the problems of diagnosis provides a significant increase in the
effectiveness of information protection management. Consideration of previous experience in
the application of artificial neural networks is successfully used in many fields, for example,
in technical and medical diagnostics [9, 10]. On a time scale close to real, artificial neural net-
works form the values of the desired characteristics, without requiring human participation in
the process of their work.
   Examples of the successful use of artificial neural networks in diagnosing failure of infor-
mation systems equipment are given in papers [11, 12]. Event logs contain data on system
failures, which are preprocessed and transmitted for trouble search to the input of artificial
neural networks.
   Papers [13, 14, 15, 16] propose an approach that uses artificial neural networks to search for
attacks and abnormal actions. High accuracy of the obtained experimental forecasts and the
ability of the forecasting system to function in a time mode close to real are noted.
   The laboriousness of the process of forming training examples for artificial neural networks
that are based on supervised learning served as an incentive for the development of deep learn-
ing, during which the neural network independently generates distinctive features for input
data sets. Effective optimization procedures using unsupervised learning were presented in
[17], which demonstrated high performance for deep neural architectures.
   Despite the fact that artificial neural networks are a powerful tool for processing data, as
evidenced by their widespread implementation in various fields of activity, the issues of au-
tomatic diagnosis of computer incidents based on artificial neural networks have not been
properly addressed in the known literature. In papers [1, 18], the authors proposed a combined
artificial neural network, which allows determining the values of the characteristic of a secu-
rity violation with high accuracy in close to real time. However, the issue of optimizing the
network structure to account for new training examples and when introducing restrictions on
the duration of training remained unexplored.
   In this paper, we propose an improved model that will eliminate these shortcomings.


3. Statement of the computer incident diagnostic task
Having discovered a computer incident, the information protection system collects data from
various sources, which include the event logs of information protection tools, servers and
workstations. Of the total volume of this data, only those that are potentially relevant to a
breach of information security are of interest. The rest are considered as information noise. In
other words, the transformation is carried out from the initial set of events X registered in the
information system to the set of informative diagnostic signs 𝑋 ,
                                                                  β€²



                                                        β€²
                                           𝐹 βˆΆπ‘‹ →𝑋 ,
where 𝑋 = {π‘₯π‘‘π‘ π‘œπ‘π‘–π‘ π‘‘ }, 𝑖𝑠𝑑 = 1, 𝑁 , π‘‘π‘ π‘œπ‘ = 1, 𝑁 , 𝑁 - number of information sources, 𝑁 - number
                                 𝑠             𝑑𝑠  𝑠                                        𝑑𝑠
of event types, 𝑋 = {π‘₯π‘‘π‘π‘Ÿ }, π‘‘π‘π‘Ÿ = 1, 𝑁𝑑𝑝 , 𝑁𝑑𝑝 - number of types of diagnostic features.
                    β€²      β€²


   Further, it is necessary to determine the values of the security violation characteristics by
the available set of diagnostic signs β„Žπ‘›π‘–π‘— ∈ 𝐻 𝑁 , 𝑖 = 1, π‘π‘β„Ž , 𝑗 = 1, 𝑁𝑧𝑛 , where π‘π‘β„Ž - the number of
security violation characteristics, the values of which must be determined during the diagnosis,
𝑁𝑧𝑛 - the number of possible values of the 𝑖-th security violation characteristic. Thus, the
solution to the diagnostic problem is to find the mapping of the set of informative events 𝑋 to
                                                                                                  β€²


the set of values of the security violation characteristics 𝐻 𝑁 , 𝐹 ∢ 𝑋 β†’ 𝐻 𝑁 .
                                                                             β€²


   The security breach characteristics are in fact a detailed description of the security violation
of information. A list of the main security violation characteristics is given in Table 1.
Table 1
Characteristics of information security violation and their meanings
                 Name of
                                             Characteristic values               Type of characteristic
               characteristic
                                     Workstation
           Object of impact          Server equipment                            primary
                                     Network hardware
                                     Information Security vulnerabilities
           Type of vulnerability     Operating System vulnerabilities            primary
                                     Application vulnerabilities
                                     The change
           Implementation            Delete
                                                                                 primary
           results                   Creation
                                     Blocking, etc.
                                     Time instant for detection of violation
           Detection time                                                        primary
                                     by information protection means
           Attack ID (computer       Name of the attack received from
                                                                                 primary
           incident ID)              information security tools
                                     Login ID
           User ID                                                               primary
                                     ID received as a result of analysis
           Attack Source             Network address and port of attack
                                                                                 primary
           Address                   source
           Attack Object             Network address, port of the object
                                                                                 primary
           Address                   of attack
                                     Information breach
           The purpose of the
                                     Violation of the integrity of information   secondary
           violation
                                     Information access violation
                                     External
           Source of violation                                                   secondary
                                     Internal
                                     Intelligence service
           Stage of                  Penetration
                                                                                 secondary
           implementation            Implementation
                                     Hiding traces
                                     Intentional
           Nature of the violation                                               secondary
                                     Unintentional
                                     Significant damage
           Result                                                                secondary
                                     Minor damage
                                     First discovered violation
           Repeatability                                                         secondary
                                     Rediscovered violation
                                     DoS attack
                                     Scanning
           Attack type                                                           secondary
                                     Computer virus
                                     Software bookmark, etc.
                                     Critical
                                     High
           Risk level                                                            secondary
                                     Average
                                     Low


   By the method of determining the values of the security violation characteristics, we divide
the characteristics into primary and secondary. The primary ones are those characteristics
whose values are determined by direct measurement or calculation (for example, user identi-
fiers, time, and others). Secondary characteristics are those for the determination of the values
of which it is necessary to build functional dependences on the values of diagnostic signs.
   To use the results of the diagnosis as new training examples, it is necessary to repeat the
training procedure. Accordingly, the problem of minimizing the time 𝑇𝑙 devoted to training
arises. At the same time, it is necessary to ensure the preservation of previously achieved
quality indicators of the artificial neural network 𝑄𝑓 . The objective function for the developed
diagnostic model can be represented as

                                       𝑇𝑙 β†’ π‘šπ‘–π‘›, 𝑄𝑛 β‰₯ 𝑄𝑓 ,
where 𝑄𝑛 - the value of the quality index of the artificial neural network after each next training,
𝑄𝑓 - the value of the quality index of an artificial neural network, which obtained during first
training.


4. Combined neural network model
To achieve the goals of diagnosing computer incidents, information is collected from numer-
ous elements of the information and communication system and the resulting picture of the
distribution of recorded events is compared with previously known distributions for which the
values of the security violation characteristics are determined.
   Due to the lack of formalized analytical dependencies between the events that have occurred
and the values of the security violation characteristics, it is proposed to use feedforward neural
networks, for example, a multilayer perceptron, to determine such dependencies. In relation
to the task of diagnosing computer incidents, a multi-layer perceptron generalizes diagnostic
signs with the subsequent determination of the values of the security violation characteristics.
   However, in order for the neural network to be able to generalize the available examples, and
not just remember them, it is necessary to strike a balance between the volume of the training
sample and the number of neurons in the structure of the neural network. To ensure compli-
ance with the quality requirements of the created neural network, it is proposed to combine
a multilayer perceptron with the encoding part of the autoencoder, that is, use a combined
artificial neural network. This architecture allows one to build a model for diagnosing com-
puter incidents that overcomes the difficulties with the formation of a large number of training
examples and allows one to adequately characterize the violation of information security.
   A model of a combined artificial neural network for diagnosing computer incidents is pre-
sented in Fig. 1, where 𝑖𝑛 - the size of input layer, π‘”π‘Ÿ - the size of the hidden layer of the
autoencoder, π‘ π‘˜ -– the size of the hidden layer of the perceptron, π‘š -– the size of the out-
put layer of the combined neural network. The ratio between the number of neurons has the
following form: 𝑖𝑛 ≫ π‘”π‘Ÿ > π‘ π‘˜ > π‘š.
   xβ€²1                                     Input layer      hidden layer       Output layer
              1
   xβ€²2                             1            1
              2
                                                                 1
   xβ€²3                             2            2
              3                                                                                {hni={0,…,1
                                                                 2                   1
                                   3            3                ...                 ...
   ...       ...                                                                               {hni={1,…,0
 xβ€²in-2                            ...         ...                                   m
            in-2                                                sk-1
                                 gr-1         gr-1
 xβ€²in-1
            in-1                                                 sk
                                  gr           gr
  xβ€²in
             in


          Coder part of the auto-encoder                    Perceptron


Figure 1: A model of a combined artificial neural network for diagnosing a computer incident



   Autoencoder, as it is known, reduces the dimension of the vector of the initial data 𝑋 arriving
at the input of a combined artificial neural network [19]. Thus, the first stage is carried out
to generalize the input data (they are compressed), i.e. πΉπ‘Ž ∢ 𝑋 β†’ 𝑋𝑔 . In the hidden layer
                                                                       β€²       β€²


of the auto-encoder, the group diagnostic features 𝑋𝑔 are formed. Then they go to the input
                                                           β€²


of the multilayer perceptron, in this case a three-layer one, which implements a procedure
for processing diagnostic signs and outputs a set of values of the π‘š-ary security violation
characteristic, i.e. 𝐹𝑝 ∢ 𝑋𝑔 β†’ 𝐻 𝑁 .
                             β€²


   Thus, the output of the considered model is an assessment of the degree of compliance
with the values of the characteristics of the security violation for the set of diagnostic fea-
tures presented at the input. By training a combined artificial neural network, the weights
of neural connections are determined 𝑀𝑖𝑗 ∈ π‘Š , 𝑖 = 1, π‘π‘π‘Ÿπ‘’π‘£ , 𝑗 = 1, π‘π‘π‘’π‘Ÿ , where π‘π‘π‘Ÿπ‘’π‘£ - – the
number of neurons in the previous layer, π‘π‘π‘’π‘Ÿ - the number of neurons in the layer under
consideration. These coefficients allow one to record in general form the dependence of the
value of the 𝑖-th security violation characteristic on the input vector of diagnostic signs 𝑋 :
                                                                                                    β€²


β„Žπ‘›π‘– = 𝑓3 (𝑓2 (𝑓1 (π‘Š1 β‹… 𝑋 ) β‹… π‘Š2 ) β‹… π‘Š3 ), where π‘Šπ‘˜ ∈ π‘Š , π‘˜ = 1, 3 - the vector of weights of the π‘˜-th
                        β€²


layer, π‘“π‘˜ - the function of activation of neurons of the π‘˜-th layer.
5. Implementation of the model
The implementation of the procedure for diagnosing computer incidents in an information
and communication system using a combined artificial neural network involves the following
sequence of actions:

    - collection and processing of data from information sources;

    - preparation of an input data set for an artificial neural network;

    - formation of group diagnostic features by the encoder part of the auto-encoder;

    - classification of the obtained group diagnostic features on the set of values of the desired
      characteristic of a security violation.

   For each secondary characteristic of a security breach, its own neural network and its own
set of training examples are formed. The result of the operation of the set of combined artificial
neural networks in parallel mode is a set of values of information security violation character-
istics, on the basis of which the development of a response option to a computer incident is
further carried out.
   The model for diagnosing a computer incident in an information and communication system
is shown in Fig. 2. After detecting a computer incident, the information security tools report
the primary security violation characteristics. At the same time, the process of determining
the secondary characteristics of a security violation is launched. The sources of information
transmit data to the feature preparation unit, where they are processed and presented to the
required form before being fed with combined artificial neural networks. Having the analy-
sis unit came, the normalized values of diagnostic features are processed in parallel mode by
several neural networks at once. At the final stage of diagnosis, a final set of values of the
characteristics of the security violation is formed, which includes the values of the primary
and secondary characteristics.
                                     Information and communication system

     Sources of
    information                               Computer Incident Diagnostic System

      Server
    Event Logs                                                             Analysis block
                                                      Block for
                                                                                                     Block for
                                                    collection and
                                                    preparation of
                                                                                            W      optimizing the   Ex   Security
    Work-station                                                                                    structure of
                                                   diagnostic signs                                                      admini-
    Event Logs                                                                                    combined neural
                          Preserving the                                     Combined                                     strator
                                                                      X’                             networks
                   X         primary           X                              ANN 1
                       characteristics of a
                        security violation         1.Filtration




                                                                                 ...
     Security                                      2.Aggregation
    Event Logs                                     3.Normalization
                                                                             Combined
                                                                              ANN n             hn (secondary)

     Network
     Hardware                                                                                    hn (primary)
    Event Logs




Figure 2: Model for diagnosing a computer incident in an information and communication system



   The set of initial data and diagnostic results can, if necessary, be used as new training exam-
ples (datasets). The number of examples in the training set 𝑁𝑒π‘₯ affects the number of neurons
in the hidden layer π‘π‘π‘˜ of an artificial neural network, according to the relation established by
R. Hecht-Nielsen [20]:
                                                                  𝑁𝑀
                                                     π‘π‘π‘˜ =              ,                                                       (1)
                                                                𝑁π‘₯ + 𝑁𝑦
                          𝑁𝑦 𝑁𝑒π‘₯                   𝑁𝑒π‘₯
                                       ≀ 𝑁𝑀 ≀ 𝑁𝑦 (     + 1)(𝑁π‘₯ + 𝑁𝑦 + 1) + 𝑁𝑦 ,                                                 (2)
                       1 + log2 (𝑁𝑒π‘₯ )             𝑁π‘₯
where 𝑁𝑦 - the number of neurons of the output layer, 𝑁𝑒π‘₯ - the number of training examples,
𝑁𝑀 - the number of neural connections, 𝑁π‘₯ - the number of neurons in the input layer.
   Accordingly, with the replenishment of the base of training examples, the structure of the
neural network should be adjusted. The choice of the number of neurons in the hidden layer
of the auto-encoder and perceptron affects the values of the quality indicators of the combined
artificial neural network and the duration of the training. In order to minimize the training
time and maintain the values of quality indicators at the required level, it is necessary to solve
the optimization problem:
                                     {
                                        𝑇𝑙 (π‘π‘π‘˜ ) β†’ π‘šπ‘–π‘›,
                                                                                                (3)
                                        𝑄𝑛 (π‘π‘π‘˜ ) β‰₯ 𝑄𝑓
  To solve this problem, computational experiments were carried out. Based on the obtained
experimental values, in the optimization unit of the structure of combined neural networks,
the optimal number of hidden layer neurons is selected and the combined neural networks are
adjusted.


6. Experimental results
An experimental assessment of the proposed model for diagnosing computer incidents was
carried out on the basis of the existing database of information security violations compiled by
experts. The database contains a description of two security violation characteristics: β€œnature
of the violation” and β€œconsequences”. It consists of 276 entries, which include sets of diag-
nostic features from event logs for 20 workstations. To characterize a security violation, the
β€œnature of the violation” of 276 records, 113 corresponds to a deliberate violation, and 163 -
to an unintentional violation. To characterize a security violation, the β€œconsequences” of the
implementation of the violation of 276 records, 164 correspond to significant damage, and 112
- to minor damage.
   Combined neural networks were implemented in the C ++ programming language. The
training was carried out on a workstation under the control of the Windows 7 Professional
operating system, 16 Gb RAM, AMD Ryzen 5 2600 processor.
   The experiments were carried out according to the following scheme. Initially, a database of
training examples was formed, which included many pairs of sets of diagnostic signs and the
corresponding values of the security violation characteristics. These pairs are designed to train
combined artificial neural networks that are part of the computer incident diagnosis model and
test their readiness for operation. Then, new training examples for subsequent adjustment of
neural networks are stored in the same database. The training is carried out by the method
of back propagation of error, during which the weighting coefficients of each communication
between artificial neurons are adjusted [21].
   Next, the structure of combined neural networks was formed. The size of the input layer for
all combined neural networks corresponds to the size of the vector of diagnostic features. To
cover the studied diagnostic features for a long period of time during the experiment, the input
layer size was 32400. The output layer of each combined neural network is determined by the
number of values of the secondary characteristic of the security violation.
   The size of the hidden layers of the autoencoder and perceptron was initially selected based
on the minimum sufficient according to R. Hecht-Nielsen’s condition (1) and (2) and amounted
to 12 and 1, respectively.
   For training and quality control of the artificial neural network, the database was divided
into two parts. Initially, 180 notes were taken for training and 76 entries for testing. The
quality assessment of the combined neural network was carried out according to the generally
accepted indicator 𝐹 -measure (𝐹 ), the value of which is calculated on the basis of indicators of
precision π‘ƒπ‘Ÿ and recall 𝑅𝑐:
                                             2 β‹… π‘ƒπ‘Ÿ β‹… 𝑅𝑐
                                         𝐹=              ,
                                              π‘ƒπ‘Ÿ + 𝑅𝑐
                                                  𝑇𝑃
                                         π‘ƒπ‘Ÿ =            ,
                                              𝑇𝑃 + 𝐹𝑃
                                                  𝑇𝑃
                                           𝑅𝑐 =          ,
                                               𝑇𝑃 + 𝐹𝑁
where 𝑇 𝑃 is the number of records classified as the true value of the characteristic, while it is
true, 𝐹 𝑃 is the number of records classified as the true value of the characteristic, while it is
actually false, 𝐹 𝑁 is the number of records classified as the false value, while it is true.
   The dependences of the values of the 𝐹 -measure indicator obtained during the computational
experiment on the number of neurons in the hidden layers of the π‘π‘Žπ‘’ autoencoder and the
π‘π‘π‘’π‘Ÿπ‘ perceptron for characterizing the security violation β€œnature of the violation” are shown
in Fig. 3, and to characterize the security violation β€œconsequences” - in Fig. 4. The combined
neural network was trained on 180 examples.




Figure 3: The values of the 𝐹 -measure indicator for the security violation characteristic β€œnature of the
violation”
Figure 4: The values of the 𝐹 -measure indicator for the security violation characteristic β€œconsequences”



   As can be seen from Fig. 3 and Fig. 4, the combined neural network reaches the maximum
value of the 𝐹 -measure index with the number of neurons of the hidden layer of the auto-
encoder of about 180 and 4 neurons of the hidden layer of the perceptron. With an increase in
the number of hidden layer neurons, an increase in the 𝐹 -measure is not observed and subse-
quently even decreases due to the occurrence of the negative effect of overfitting.
   By increasing the number of examples to 194 and testing on 82 examples, the task of op-
timizing the training time of a neural network is solved by choosing the minimum sufficient
number of hidden layer neurons without losing the quality of the originally created network.
The combined neural network has high values of the accuracy indicator for determining the
value of the binary characteristic of a security violation with the number of neurons 186 for
the hidden layer of the auto-encoder and 4 for the hidden layer of the perceptron. With an in-
crease in the number of neurons, the training time increases, and the values of the accuracy and
completeness indicators initially remain the same, but then decrease. With a decrease in the
number of neurons of the hidden layers, along with a slight decrease in the training time, the
values of the accuracy and completeness indicators decrease. That is unacceptable according
to the conditions of the problem.
   These results indicate the need to adapt the structure of the combined neural network when
replenishing the base of training examples. While for the number of training examples up to
200, the number of neurons in the hidden layer of the auto-encoder is advisable to choose about
185, the number of neurons in the hidden layer of the perceptron is 4. With an increase in the
number of training examples by 14, the values of the 𝐹 -measure indicator remained the same
with an increase in the number of neurons of the hidden layer of the auto-encoder by 6 and
the preservation of 4 neurons of the hidden layer of the perceptron.
   In comparison with a multilayer perceptron, a combined neural network allows us to ensure
that the requirements for the 𝐹 -measure and training time are met, the values of which are
given in Table 2. In this paper, training time the combined neural network is defined as the
time period after which the specified requirement for the difference between the received and
known output values of the network for all training examples is fulfilled.

Table 2
Comparison of the indicators 𝐹 -measure and training time for neural network
                                         Multilayer                  Combined neural
               Number of
                                         perceptron                     network
           training examples
                                              Training time,               Training time,
                                𝐹 -measure                     𝐹 -measure
                                                   min                           min
                  140               0.70          76.10            0.89         10.32
                  160               0.72          79.08            0.90         10.76
                  180               0.72           83.2            0.91         11.01
                  194               0.72          84.07            0.91         11.17

   Thus, the requirement according to expression 4.3 is met. As can be seen from Table 2, the
training of a multi-layer perceptron takes much longer on a small number of examples and does
not ensure the achievement of the values of the 𝐹 -measure indicator for a combined artificial
neural network.


7. Conclusion
The paper proposed a new model for diagnosing computer incidents based on combined neural
networks, and attempted to solve the problem of optimizing the structure of combined neural
networks in order to minimize training time when adding new training examples.
   The use of an auto-encoder as part of the combined neural network allowed one to switch
from an input set of high-dimensional diagnostic features to a compact representation due
to compression using the principal component method. The resulting set of group diagnostic
features is classified according to the set of values of the characteristics of the security violation.
The classification problem is solved by a three-layer perceptron. Reducing the dimension of a
set of diagnostic features allows the training of a combined neural network on a fairly small
base of training examples.
   An experimental evaluation of the proposed model on a test bench made it possible to iden-
tify the optimal number of neurons in the hidden layers of the combined neural network in the
interest of minimizing the training time.
   Given the simplicity of the proposed model, it seems possible its practical application as part
of the information protection system of a typical information and communication system.
   The directions of further research are associated with the study of the use of combined neu-
ral networks to determine the values of the secondary characteristics of information security
violations, depending on other previously defined characteristics, including primary ones, by
adding recurrent neural networks to the structure. It is also interesting to study the effect
of dropout for neurons of hidden layers of the combined neural network on the value of the
𝐹 -measure indicator.
Acknowledgments
This research is being supported by the grant of RSF #18-11-00302 in SPIIRAS.


References
 [1] A. Malikov, V. Avramenko, I. Saenko, Model and method for diagnosing computer inci-
     dents in information and communication systems based on deep machine learning, In-
     formation and Control Systems 103 (2019).
 [2] R. Vaarandi, A data clustering algorithm for mining patterns from event logs, in: Pro-
     ceedings of the 3rd IEEE Workshop on IP Operations & Management (IPOM 2003)(IEEE
     Cat. No. 03EX764), IEEE, 2003, pp. 119–126.
 [3] Z. Kurd, Artificial neural networks in safety-critical applications, Ph.D. thesis, University
     of York, 2005.
 [4] H.-J. Cheng, A. Kumar, Process mining on noisy logsβ€”can log sanitization help to improve
     performance?, Decision Support Systems 79 (2015) 138–149.
 [5] R. J. C. Bose, R. S. Mans, W. M. van der Aalst, Wanna improve process mining results?,
     in: 2013 IEEE symposium on computational intelligence and data mining (CIDM), IEEE,
     2013, pp. 127–134.
 [6] V. I. Gorodetski, O. Karsayev, A. Khabalov, I. Kotenko, L. J. Popyack, V. Skormin, Agent-
     based model of computer network security system: A case study, in: International
     Workshop on Mathematical Methods, Models, and Architectures for Network Security,
     Springer, 2001, pp. 39–50.
 [7] I. Kotenko, O. Polubelova, I. Saenko, The ontological approach for siem data repository
     implementation, in: 2012 IEEE International Conference on Green Computing and Com-
     munications, IEEE, 2012, pp. 761–766.
 [8] I. Kotenko, I. Saenko, Creating new-generation cybersecurity monitoring and manage-
     ment systems, Herald of the Russian Academy of Sciences 84 (2014) 424–431.
 [9] I. Bogachev, A. Levents, E. U. Chye, Application of an artificial neural network for classi-
     fication of telemetric data in compression systems, Information and Control Systems 82
     (2016).
[10] M. V. Vyucheyskaya, I. N. Kraynova, A. V. Gribanov, Neural network technologies in
     medical diagnosis (review). p. 284–294, Medical biology research 3 (2018) 284–294.
[11] F. Lv, C. Wen, Z. Bao, M. Liu, Fault diagnosis based on deep learning, in: 2016 American
     Control Conference (ACC), IEEE, 2016, pp. 6851–6856.
[12] D.-Q. Zou, H. Qin, H. Jin, Uilog: Improving log-based fault diagnosis by log analysis,
     Journal of computer science and technology 31 (2016) 1038–1052.
[13] Q. Fu, J.-G. Lou, Y. Wang, J. Li, Execution anomaly detection in distributed systems
     through unstructured log analysis, in: 2009 ninth IEEE international conference on data
     mining, IEEE, 2009, pp. 149–158.
[14] T. Nolle, A. Seeliger, M. MΓΌhlhΓ€user, Unsupervised anomaly detection in noisy business
     process event logs using denoising autoencoders, in: International conference on discov-
     ery science, Springer, 2016, pp. 442–456.
[15] M. Sakurada, T. Yairi, Anomaly detection using autoencoders with nonlinear dimension-
     ality reduction, in: Proceedings of the MLSDA 2014 2nd Workshop on Machine Learning
     for Sensory Data Analysis, 2014, pp. 4–11.
[16] M. Alkasassbeh, An empirical evaluation for the intrusion detection features based on
     machine learning and feature selection methods, arXiv preprint arXiv:1712.09623 (2017).
[17] H. Larochelle, D. Erhan, A. Courville, J. Bergstra, Y. Bengio, An empirical evaluation of
     deep architectures on problems with many factors of variation, in: Proceedings of the
     24th international conference on Machine learning, 2007, pp. 473–480.
[18] V. Avramenko, A. Malikov, Diagnosing computer security incidents based on a combined
     artificial neural network, Information Security. Inside (2019) 72–76.
[19] P. Baldi, Autoencoders, unsupervised learning, and deep architectures, in: Proceedings
     of ICML workshop on unsupervised and transfer learning, 2012, pp. 37–49.
[20] R. Hecht-Nielsen, Kolmogorov’s mapping neural network existence theorem, in: Pro-
     ceedings of the international conference on Neural Networks, volume 3, IEEE Press New
     York, 1987, pp. 11–14.
[21] S. Khaikin, Neural networks: full course, M.: Williams 1104 (2006).