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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Adversarial Entry in Finance through Credit Card Fraud Detection</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Akshay Agarwal</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
          <xref ref-type="aff" rid="aff2">2</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Nalini Ratha</string-name>
          <email>nratha@bufalo.edu</email>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
          <xref ref-type="aff" rid="aff2">2</xref>
        </contrib>
        <contrib contrib-type="editor">
          <string-name>Adversarial Attacks, Credit Card Fraud Detection, Machine Learning Classifiers, Vulnerability, Black-Box,</string-name>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>In this research, for the first time</institution>
          ,
          <addr-line>we have extensively</addr-line>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>University at Bufalo</institution>
          ,
          <country country="US">USA</country>
        </aff>
        <aff id="aff2">
          <label>2</label>
          <institution>Workshop Proce dings</institution>
        </aff>
      </contrib-group>
      <abstract>
        <p>In the literature, it is well explored that machine learning algorithms trained on image classes are highly vulnerable against adversarial examples. However, very limited attention has been given to other sets of inputs such as speech, text, and tabular data. One such application where little work has been done towards adversarial examples generation is financial systems. Despite processing sensitive information such as credit fraud detection and default payment prediction, a low depiction of the robustness of the financial machine learning algorithms can be dangerous. One possible reason for such limited work is the challenge of crafting adversarial examples on the financial databases. The financial databases are heterogeneous where features might have a strong dependency on each other. Whereas image databases are homogeneous, and hence several existing works have shown it is easy to attack the classifiers trained on them. In this paper, for the first, we have analyzed the vulnerability of several traditional machine learning classifiers trained on financial tabular databases. To check the robustness of these classifiers, ' black-box and classifier agnostic ' adversarial attack is proposed through mathematical operations on the features. In brief, the proposed research for the first time presents a detailed analysis that reflects which classifier is robust against minute perturbation in the tabular features. Apart from that through the perturbation on individual features, it is shown which column feature is more or less sensitive for the incorrect classification of the classifier.</p>
      </abstract>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>-</title>
      <p>
        evaluated several machine learning models and their
vulutilize the power of machine learning (ML) algorithms. due to no drastic change in the feature space and hence
[
        <xref ref-type="bibr" rid="ref6">6, 7, 8</xref>
        ] and solving complex medical problems [9, 10, 11]. ing small modifications. The severity of the credit fraud
algorithms are highly susceptible against the minute per- amount, the United Stated is one of the largest
contribu
      </p>
    </sec>
    <sec id="sec-2">
      <title>1. Introduction</title>
      <p>
        The recent research articles claim that in the last decade
from 2010 to 2020, people with the personal loan double
from $11 million to $21 million [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. At the same time,
the amount of loan debt increase by three times from
$55 billion to $162 billion. The processing of such a large
number of loan applications and identifying any possible
fraud is a tedious and time-consuming task for a human
being. The possible solution to overcome the load is to
      </p>
      <sec id="sec-2-1">
        <title>In the past, machine learning algorithms have shown tremendous success in solving variety of tasks ranging from object recognition [4, 5] to person identification</title>
      </sec>
      <sec id="sec-2-2">
        <title>While the machine algorithms are here to ease the human and perform the task with near perfection. However, recent research indicates that the machine learning turbation in the input data.</title>
        <p>Imagine a scenario, where a corrupt individual came
into the bank for credit card approval and the issue of a
In International Workshop on Modelling Uncertainty in the Financial
World (MUFin21) In conjunction with CIKM 2021,</p>
        <p>https://sites.google.com/iiitd.ac.in/agarwalakshay/home
(A. Agarwal); https://nalini-ratha.github.io/ (N. Ratha)
0000-0001-7362-4752 (A. Agarwal); 0000-0001-7913-5722
© 2021 Copyright for this paper by its authors. Use permitted under Creative
(N. Ratha)
nerability against minute perturbations in the feature the databases. Later, the machine learning classifiers
space (or input space). The credit card default prediction chosen to perform the vulnerability analysis are
dedatabases contain multiple features such as age, gender, scribed. The experimental results along with analysis
payment status, and education. The individual feature are presented to showcase the impact of the proposed
can afect the classification decision due to any reason ‘black-box and classifier agnostic’ adversarial
perturbasuch as bias and mislabelling. For example, it might tion.
be believed that the highly educated individual might
not perform fraud. Therefore, in this research, we have
identified the sensitivity of various machine learning clas- 2. Existing Adversarial Examples
sifiers against individual features both in their raw form Research
and under minute perturbation. While the features play
an important role, the optimization function of diferent Since the finding of adversarial examples [ 14], several
classifiers play an important role in learning decision adversarial attack algorithms are presented in the
literboundaries. Hence, the detailed experimental evaluation ature. The existing adversarial attacks can be divided
of multiple machine learning classifiers has been per- based on the following two criteria: (i) intention and (ii)
formed to showcase which classifier is more robust or type of learning. The type of learning can be described
sensitive against imperceptible perturbations. In brief, how much knowledge of the machine learning
classithe contributions of this research are: ifer is needed to fool it and it can be categorized into
white-box and black-box. In the white-box setting, an
• first-ever black-box inference time imperceptible attacker assumes the complete knowledge of the system
adversarial attack on credit-card default predic- such as its parameters and classification probabilities. On
tion is performed; the other hand, the black-box attacks do not utilize any
• extensive ablation studies are conducted to find ML network information in creating adversarial
examout the importance of individual feature value ples. In the real world, it is extremely dificult to acquire
towards decision making; the knowledge of the machine learning classifiers due
• sensitivity analysis of multiple machine learning to their security and the existence of a wide variety of
classifiers are presented to help in building a ro- machine learning algorithms. For example, Goel et al.
bust finance system utilizing robust classifier(s); [15, 16, 17] have utilized the concept of blockchain and
• comprehensive survey of the existing adversarial cryptography to either change the structure of the
netattacks developed in other data domains show- works or encrypt them to make it dificult to identify the
case the needs of the development of adversary exact parameters of the networks. Similarly, there exists
to identify the vulnerabilities in the finance space a humongous number of machine learning algorithms
as well. such as supervised, unsupervised, and ensemble learning,
hence, assuming the knowledge of the system an attacker</p>
        <p>In the next section, the review of the existing adver- wants to fool is dificult [ 18, 19]. Due to the above
obsersarial examples is presented followed by the descrip- vations, a black-box attack is practical in the real world
tion of credit card default prediction databases. In and at the same dificult to achieve. On the other hand,
the next, exploratory database analysis has been per- intention-based attacks are divided into targeted attacks
formed to efectively examine the characteristics of and untargeted attacks. The targeted attacks aim the
input data to be misclassified by the network into one of Table 1
the desired classes. For example, a credit card defaulter Characteristics of the Credit Card databases.
would like to be classified as genuine by the machine Default Credit Australian Credit
learning classifier. Whereas, the untargeted attacks aim Feature Name Type Feature Type
the input data to be misclassified into ‘any’ class except 21 ILDimit-Bal CCoonnttiinnuuoouuss AA12 BCionnatriynuous
the true class. 3 Sex Binary A3 Continuous</p>
        <p>In the literature, several adversarial attacks are pro- 45 EMdaurcraiatgioen CCaatteeggoorriiccaall AA45 CCaatteeggoorriiccaall
posed. The majority of the attacks are proposed for visual 6 Age Continuous A6 Categorical
object classification and limited work has been done so 7 Pay_0 Continuous A7 Continuous
far for other kinds of input information such as speech 98 PPaayy__23 CCoonnttiinnuuoouuss AA89 BBiinnaarryy
and tabular data, and machine learning classifiers such 10 Pay_4 Continuous A10 Continuous
as reinforcement learning. The gradient is one of the 1121 PPaayy__56 CCoonnttiinnuuoouuss AA1112 BCiantaergyorical
most essential information in deep network learning and 13 Bill_Amt1 Continuous A13 Continuous
utilizing this information several attacks are proposed. 14 Bill_Amt2 Continuous A14 Continuous
For example, PGD attack [20] is one of the strongest 1156 BBiillll__AAmmtt34 CCoonnttiinnuuoouuss A15 Binary
attacks for visual image classifiers. The attack is per- 17 Bill_Amt5 Continuous
formed in multiple iterations by projecting the gradient 18 Bill_Amt6 Continuous
in the direction that leads to the strong adversary. Other 1290 PPaayy__AAmmtt12 CCoonnttiinnuuoouuss
image-based attacks such as DeepFool [21], add the per- 21 Pay_Amt3 Continuous
turbation in the image iteratively so that the image can 2232 PPaayy__AAmmtt45 CCoonnttiinnuuoouuss
pass its corresponding class decision boundary learned 24 Pay_Amt6 Continuous
by the network. The above attacks learn the manipu- 25 Default Payment Binary
lation for each image separately, while it is possible to
learn a unique noise vector to apply on multiple images
and fool the network [22, 23]. The above-described at- efectively. Agarwal et al. [ 28] have not utilized any
extertacks are performed in the white-box setting utilizing the nal knowledge including perturbation vector but extract
complete knowledge of the classifier. Another disadvan- the noise inherently present in an image. The authors use
tage of the white-box attack is the transferability against an intelligent observation that due to several factors such
multiple models. As the attacks are generated utilizing as camera preprocessing steps, environmental factors,
the knowledge of the classifier which can be significantly the noise inherently present in an image. The authors
diferent from the other unseen models, hence, leads to a extract those noise pattern and used as an adversarial
poor success rate against unseen models [24, 25]. pattern. The above-mentioned attacks are performed in</p>
        <p>The other class of attack is the black-box attacks which the image space. Limited attacks are also proposed in
are more practical in the real world and can fool multiple other categories of networks or input such as generative
classifiers. The black-box attack can be further divided models [29], reinforcement learning [30], and cyberspace
into query-based and generic manipulation-based. In [31].
the query-based attack, some knowledge of the system While on the one hand, adversarial attacks on machine
is assumed such as the decision of the classifier. By uti- learning classifiers especially deep learning classifiers
lizing the decision of the classifier on the given input, are prevalent, the defense against them is also getting
the noise is modified leading to the desired intent of significant attention. Several defense algorithms based
misclassification, i.e., targeted or untargeted. While the on the following two motives are proposed: (i)
segregaquery-based attacks are more successful for unseen mod- tion of the adversarial examples from the clean examples
els whose knowledge is not available but still bounded [32] and (ii) mitigating the impact of adversarial noise
by the number of queries that can be sent for the noise [27]. The defense algorithms have shown tremendous
generation. Therefore, this limitation restricts the practi- success in countering the adversarial attacks on the
imcal deployment at multiple places. Another category of age domain and show generalizability even in complex
attack which is general manipulation is one of the most situations such as an unseen attack, unseen database,
successful attacks because not utilization of any classifier and unseen model [33, 34]. The survey of the existing
knowledge makes them agnostic to classifiers and can research on adversarial examples can be further referred
fool multiple classifiers. Goswami et al. [ 26, 27] have from the survey papers [35, 36, 37].
proposed several image manipulations for fooling face It is interesting to observe from the above discussion
recognition networks. The manipulations are somewhat that adversarial machine learning is one of the fasted
inspired by the domain knowledge of face recognition growing communities; however, only a few works
exand therefore, modified the landmark features of a face ist towards the robustness in the financial domain. The
image which were able to fool the recognition networks prime reason for such low existence can bethink from
the point of the type of input. The financial data espe- operators. The proposed attacks work in the black-box
cially tabular databases are heterogeneous as compared setting and do not utilize any information of a classifier.
to homogeneous image databases. Tabular features are Therefore, the proposed attack is classifier agnostic and
not interchangeable in contrast to the pixels of an image. can be applied against ‘any’ classifier. In contrast to the
Apart from that, the images are rich in visual informa- existing research reported on the limited classifier, the
tion and hence humans can predict the information by proposed research study the adversarial strength against
looking at them and easy to identify whether any manip- multiple classifiers and shows that the proposed attack
ulation has been performed. Whereas tabular data are can fool each of them. Apart from this, the proposed
less interpretative and it is complex to identify the minor manipulation also aims to reveal the role of individual
modification in individual value. In the literature, few re- tabular features in the classification.
search works are proposed for crafting adversarial noise
on tabular databases. Ballet et al. [38] and Levy et al.
[39] have proposed an imperceptible adversarial attack 3. Finance Databases
by minimizing the norm of the perturbation. The
critical drawback of the attacks is that the attacker assumes
the complete knowledge of the classifier for learning the
perturbation and hence less practical for real-world
deployment. Another drawback is that the norm-based
perturbation on the tabular features can yield unrealistic
transformations [40]. Apart from that, the above attacks
on tabular data are evaluated on a single classifier, i.e., a
shallow neural network or decision forest.</p>
        <p>To overcome the limitations of the existing adversarial
study on the tabular databases, we have proposed an
adversarial manipulation method based on mathematical</p>
      </sec>
      <sec id="sec-2-3">
        <title>In this research, we have used two popular credit</title>
        <p>card default prediction databases namely Default Credit
Database [41, 42] ad Australian Credit Database [12]. The
default credit database is one of the largest databases for
the binary prediction of the default payment category.</p>
        <p>The database contains 30, 000 data points belonging to
two categories of default payment, i.e., yes or no. In
total, the database consists of 24 features belonging to
multiple types such as binary (0 or 1), categorical (1 to
 ), and continuous. The ID is a feature to represent an
individual in the database and hence no role in the
classification of the data point. Therefore, the ID feature is
4.1. Correlation Analysis
discarded from the Default Credit database. It is clear
from the description that each feature has a diferent
scale and hence, it is important to bring each feature
into the same range, such as between 0 to 1. We have
performed the min-max normalization to bring the scale
of each feature to the same range. The Australian Credit
database contains 14 features aiming to classify the data
into binary categories of default payment. Similar to the
Default Credit database, the Australian database consists
of the features of diferent scales and hence normalized
using min-max scaling. The characteristics of both the
databases are given in Table 1. Contrary to few available
pieces of research [38] which drops few features for
adversarial learning on credit database, we have utilized
each feature in the database and analyze their impact on
adversary generation.</p>
        <p>Figure 2 shows the correlation heatmap among each
feature in the Default Credit Card database. It is clear from
the heatmap that, no feature exhibits a strong correlation
with the class variable (default payment). Whereas, the
features that belong to the same category such as ‘Pay_’
and ‘BILL_AMT’ show a strong correlation among
themselves. For example, ‘Pay_0’ have the positive correlation
value of 0.67 with variable ‘Pay_1’. ‘Pay_0’ feature
represents the repayment status in September 2005 and the
value of the feature ranges between -1 to 9. Other pay
features represent the repayment status between April
to August 2005. The correlation among them shows the
repayment status of the current month and in turn, the
credit default payment is somewhat dependent on the
status of the last month. However, as compared to
repayment status, ‘BILL_AMT’ features have very strong
4. Exploratory Data Analysis correlation values among themselves. The correlation
value of at least 0.8 is observed between diferent features.</p>
        <p>Before performing the adversarial attack on the input ‘BILL_AMT’ represents the amount of bill statement
befeatures of the Credit Card databases, we have performed tween April 2005 to September 2005.
the exploration studies on the features such as correlation
among the features and relevance of the features.
4.2. Feature Importance goal of selecting the important features by reducing the
redundancy among the features and weighting the
releAnother data exploratory analysis has been performed vant features. For that, the MRMR algorithm computes
by examining the importance of individual features con- the mutual information among the features and between
cerning the class label. For that two feature selection or feature and class label. The MRMR algorithm selects the
feature weight assignment algorithms namely Univari- best feature set ( ) for classification by maximizing the
ate Feature Ranking (UFR) and Minimum Redundancy relevance score |  | between feature  and class label  .
Maximum Relevance (MRMR) [43], are utilized. The At the same time, the algorithm aims to minimize the
advantage of both the algorithm is that they accept cat- redundancy score |  | between two feature values  and
egorical and continuous features for the classification  . The |  | and |  | can be defined using the following
problem. The UFR algorithm measures the independence equations:
cohfie-saqcuhafreeatteusrtebceotwnceeenrntihnegmt.hTehcelassms avlalerriatbhleepu-vsianlugetohne   = 1 ∑  (,  )
a particular feature represents the higher the dependence || ∈
between the feature and class label and the importance   = 1 ∑  (, )
of the feature for classification. MRMR algorithm itera- || 2 ∈
tively examines the features to find the features which where, || represents the number of features in the
optiare mutually and maximally dissimilar to each other but mal subset  . Finally, mutual information quotient (MIQ)
efective for decision making. The algorithm achieves its</p>
        <p>Adversarial vulnerability of multiple machine learning classifiers against the proposed perturbation defined in Equation 1
on Australian Credit Card Database. Colored box represents the sensitive features and drop in accuracy of classifier on the</p>
        <sec id="sec-2-3-1">
          <title>Logistic</title>
        </sec>
        <sec id="sec-2-3-2">
          <title>Regression</title>
        </sec>
        <sec id="sec-2-3-3">
          <title>Binary</title>
        </sec>
        <sec id="sec-2-3-4">
          <title>Trees</title>
        </sec>
        <sec id="sec-2-3-5">
          <title>Neural Network</title>
        </sec>
        <sec id="sec-2-3-6">
          <title>Shallow</title>
        </sec>
        <sec id="sec-2-3-7">
          <title>Perturb</title>
          <p>Feature
1
2
3
4
5
6
7
8
9
10
11
12
13
14</p>
          <p>SVM
Linear
where,   and   are the relevance and redundancy value</p>
          <p>The earlier adversarial studies discarded few features
and hence do not provide the complete picture on the
credit card domain. We want to highlight that the
proposed research is the first work explaining detailed
analysis helpful both crafting the attack and mitigating it by
protecting the important features. Figure 3 and Figure</p>
        </sec>
      </sec>
      <sec id="sec-2-4">
        <title>4 show the score plot of the features from the Default</title>
      </sec>
      <sec id="sec-2-5">
        <title>Credit and Australian Credit Card database, respectively.</title>
      </sec>
      <sec id="sec-2-6">
        <title>On the Default Credit database, feature 6 (i.e., Age as</title>
        <p>shown in Table 1) shows the highest importance
irrespective of the feature selection algorithm. Feature 8 is found
most relevant in the Australian database using both UFR
and MRMR feature selection algorithms.</p>
      </sec>
    </sec>
    <sec id="sec-3">
      <title>5. Vulnerable Machine Learning</title>
    </sec>
    <sec id="sec-4">
      <title>Algorithms</title>
      <p>In this research, we have used several machine learning
algorithms to carefully investigate the impact of
adversarial manipulation on the feature space of Credit Card
databases. To present a first-ever detailed study, in total,
nine diferent classifiers are used for extensively
investigating the adversarial fraud in the finance domain.
Further, we describe each of the algorithms used for binary
classification on clean and manipulated features:
Deep
the model. The probability of each class can be
computed using the following logistic formula:
 ( ) =</p>
      <p>exp  0 +  1 1 + ...... +    
6. Proposed Adversarial Attack</p>
      <p>and Experimental Results</p>
      <p>In this section, we describe the adversarial
manipulation results and analysis using the constant value
modification as the attack. The databases are divided into
training and testing, where the training set contains
randomly selected 75% of the total data point. The remaining
25% data points are used for the evaluation of each of the
classifiers trained on the training set.</p>
      <p>The analysis of the results can be divided into the
following parts: 1 accuracy on the clean images, 2
robustness of a classifier, and 3 sensitive features for
adversarial goal. The credit card default payment results
of each classifier on a clean test of both the databases
are reported in Figure 5. On the Australian database, as
compared to the non-linear classifiers such as RBF SVM
and Neural Network, the linear classifier such as linear
SVM performs better. Whereas, on the default credit
card database, the RBF SVM performs best as compared
to other linear and non-linear classifiers. It is interesting
to note from going shallow to a deep neural network,
no significant improvement in accuracy notices on both
the databases. In another observation, the Naive Bayes
classifier performs the worst on the Australian credit
card database and second-worst on the default credit
card database.</p>
      <p>Analysis concerning classifiers: In terms of the
sensitivity of the classifier, it is found that the SVM classifier is
the least robust in terms of the magnitude of the accuracy
( −   )|Σ |−1
(
−1
2
((2 )  |Σ |)1/2
 (|) =</p>
      <p>( −   ) )
drop on both Australian credit card and default credit Analysis concerning features: The default payment
card databases. On the Australian database, the accuracy database contains 23 features by removing the ID
feaof the linear SVM drops from 86.13% to 13.88%. The rela- ture which is simply a sequence reflecting the
obsertive drop in the accuracy is 72.25% which is the highest vation number and class variable, i.e., default payment.
among all the classifiers used for credit default predic- Whereas, the Australian database contains 14 features for
tion. On the other hand, the Naive Bayes classifier which classification. We want to mention that in this research,
performs the worst on the Australian database shows the we have shown the adversarial strength by perturbing
least drop in accuracy when the features are perturbed a single feature only. On the Australian database,
feausing the proposed black-box and model agnostic attack. ture 8 is found most sensitive feature, and perturbing
In other words, the Naive Bayes classifier is found most that feature afects the performance of each classifier
efective in handling the perturbation. The accuracy of significantly. Apart from afecting the performance of
each classifier on the clean images, least accuracy ob- each classifier, feature 8 shows the highest reduction in
tained under perturbation, and diference reflecting a the accuracy of each classifier. Feature 8 contains the
maximum drop in the accuracy is reported in Figure 6 binary values and we have modified the binary values
(left) on the Australian database. On the default credit through the ‘XOR’ operator as shown in the proposed
card database, the non-linear RBF classifier found the attack equation 1. The second worst feature is the
feahighest vulnerable and the relative drop in the perfor- ture 14 which contains the continuous values. However,
mance is went to 60.3%. KNN classifier is found most interesting both linear and non-linear SVM, binary trees,
robust in terms of the relative drop in the performance and deep neural networks are found robust against the
when the features are compared as compared to the ac- slight modification on it.
curacy on the clean features. It is interesting to note On the default credit card database, feature 6 found
that, even on the Australian database, KNN shows the the weakest point of each classifier except for shallow
second-best robustness on the perturbed features. Figure neural network (S-NNet). The perturbation of the
fea6 (right) shows the maximum sensitivity of each classifier ture 6 significantly dropped the accuracy of the afected
on the default credit card database. classifiers. The RBF SVM classifier is found sensitive
against feature 6 only. We want to highlight that both perturbation can be defined in the terms of the
numthe feature selection algorithms give the highest score to ber of values available for manipulation. For example,
the features 6 as shown in Figure 3 on the default credit an image contains a significantly large number of
valcard database. Similarly, on the Australian database, each ues (pixels) available for manipulation and is easily
inclassifier has been found highly sensitive to the highest terchangeable. Whereas, the tabular finance databases
relevance features reported by the feature selection al- contain a low number of features and can not be easily
ingorithms as shown in Figure 4. The detailed analysis on terchanged with each other. Few works exist to identify
the sensitivity of individual features is given in Tables 2 the vulnerability of ML algorithms on tabular databases.
and 3. However, limitations of the existing attacks are that they
Other Manipulations: We want to highlight that the require white-box access of the classifiers and result in
other mathematical operations such as  and  men- unwanted transformations of the features. In this
retioned in Section 6 yield similar adversarial phenomena search, we have proposed a first-ever black-box attack
are observed on each classifier. on the tabular credit card default prediction databases.
We have evaluated a broad number of machine learning
6.1. Unwanted Phenomena for Attacker classifiers as compared to a few classifier vulnerability
assessments in the existing works. The proposed attack
proves its classifier agnostic strength by fooling each
classifier. Apart from the evaluation of multiple classifiers,
we have also studied the sensitivity concerning
individual features of the databases. Interestingly, it is observed
that perturbation of every feature might hurt the aim
of an attack, and therefore, intelligent consideration is
required. We hope the proposed research opens multiple
research threads both towards finding the vulnerabilities
of tabular classifiers and improving their robustness.</p>
      <p>It is interesting to observe that the adversarial
perturbation does not always reduce the performance of a
classifier. Apart from that, another interesting point is that
the features which are least important for classification,
perturbing them can inversely afect the goal of an
attacker. The importance of the features can be calculated
using the feature selection algorithm. For example, on
the Australian database, the feature 11 was found least
relevant by both UFR and MRMR feature selection
algorithm. Interestingly, perturbing this feature significantly
improves the performance of multiple classifiers. For
example, the performance of the RBF SVM, logistic
regression, and shallow neural network (S-NNet) improves
by 2.89%, 1.73%, and 2.31%, respectively. Similarly, the
features which are found less relevant by the feature
selection algorithms on the default database, perturbing
them shows the performance improvement. For example,
features 1 and 14 are among the least important feature in
the default payment database. However, perturbing them
drastically increased the performance of the Naive Bayes
classifier. The performance of Naive Bayes shows at
least 5.55% jump in the classification performance when
perturbing these features. From the above analysis, we
suggest careful attention is required while perturbing a
feature, a random perturbation of any feature set might
not be fruitful for an attacker. Although further analysis
can reveal future directions to improve the performance
of a classifier by securing only the relevant features.</p>
    </sec>
    <sec id="sec-5">
      <title>7. Conclusion</title>
      <p>Adversarial vulnerability of the visual classifiers is
extensively explored and paves the way for improving their
robustness for secure real-world deployment. However,
limited work has been done on financial databases
especially tabular databases. The probable reason might
be the heterogeneous nature of the databases and the
low degree of freedom for perturbation. The degree of
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