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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Eficient Malware Analysis Using Metric Embeddings</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Ethan M. Rudd</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>David Krisilof</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Daniel Olszewski</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Edward Raf</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>James Holt</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Mandiant Inc.</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Booz Allen Hamilton</string-name>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Laboratory for Physical Sciences, University of Maryland</institution>
          ,
          <country country="US">USA</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>Machine learning-based malware classification has become a key component of modern defense-in-depth strategies, with focus placed on the binary classification task of malware detection. These detection models are typically combined with other toolchains, which provide additional context necessary for triage and remediation, including detection names, capability, and type information. The resulting systems are often complex and interconnected, incurring significant technical debt, infrastructure costs, and inevitable errors. In this paper, we examine the feasibility of using machine learning to streamline malware analysis pipelines in a manner which minimizes potential risks and costs while preserving flexibility and functionality. To this end, we explore the use of metric learning to embed malicious and benign samples in a low-dimensional vector space with enriched capability information for downstream use in a variety of applications, including detection, family classification, and malware attribute classification. Specifically, we enrich labeling on malicious and benign PE files from the EMBER dataset using Mandiant's CAPA tool, an open-source toolchain which uses disassembly and subject matter expert (SME) derived rules and heuristics to determine malicious capabilities. Using these CAPA labels, we derive several diferent types of metric embeddings utilizing an embedding neural network trained via contrastive loss, Spearman rank correlation on malware similarity, and combinations thereof. We then examine performance on a variety of transfer tasks performed on the EMBER and SOREL datasets. We show that for a variety of transfer tasks, we are able to utilize relatively low-dimensional metric embeddings with little decay in performance, which ofers the potential to quickly retrain for a variety of transfer tasks. The low-dimensional representations ofer added potential to significantly reduce training and storage overhead when performing retrains or transferring to additional downstream tasks.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Metric Embeddings</kwd>
        <kwd>Machine Learning</kwd>
        <kwd>Malware Analysis</kwd>
        <kwd>Information Security</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        Malware analysis is a complex process involving highly skilled experts and many person-hours. Given
the number of new files seen each day (more than 500,000 on VirusTotal alone [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]) automation of
malware analysis is a necessity. Development of new analysis tools provides an avenue for more eficient
malware analysis teams.
      </p>
      <p>Fortunately, malware analysis tasks are often amenable to machine learning (ML) solutions. The
tasks (e.g., malware detection or malware family classification) are complex enough that traditional
rules-based approaches remain brittle and require frequent updating. At the same time, it is possible to
acquire and label large data sets to train ML models using threat feeds and crowdsourcing services, like
VirusTotal or Reversing Labs.</p>
      <p>
        One notable downside, however, is that ML models come with significant technical debt: they need
to be retrained as malware evolves and often interdependencies between various model components
can be hard to understand or predict [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. Even with a consistent feature vector representation, when
training on industry-scale datasets, feature stores may require tens of terabytes and model re-training
can take multiple weeks.
      </p>
      <p>This motivates the question: what if we can use ML to derive low-dimensional representations which
capture semantic behavior of malware/goodware that can be used to speed up and reduce resource
requirements for downstream tasks? This could significantly enhance capability for training classifiers
for novel applications, performing rapid iteration/experimentation, and eficiently updating deployed
models, all at reduced processing and storage requirements.</p>
      <p>Since other applications of applied ML, including biometrics and information retrieval (IR) systems,
have utilized metric learning to derive low-dimensional embeddings for similar downstream tasks, in
this paper, we explore whether we can apply metric learning in a similar vein towards various malware
analysis-oriented ML tasks. Using metric embeddings, we aim to simplify some of the engineering costs
associated with running and maintaining a suite of diferent downstream ML tooling.</p>
      <p>
        Contrary to other applications of ML classification, where data can trivially be assigned labels
corresponding to one or more classes/attributes, labeling for malware analysis tasks can be more
dificult [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. Moreover, data for malware analysis often includes telemetry and metadata beyond hard
labels which could ideally be used to enrich our metric embeddings. In this paper, we explore techniques
to enrich our embeddings with complex semantic information provided by computationally-expensive
tools (e.g., disassembly). This allows us to explore whether it is possible to approximate more expensive
analysis with lower-overhead static representations.
      </p>
      <p>When generating our embeddings, we utilize Mandiant’s CAPA tool; an open source tool, which
utilizes rules and heuristics in conjunction with disassembly to yield capability labels (e.g., file read/write,
registry key generation, process creation, data send/receive over networks, socket connection, base64/XOR
encoding) associated with a given PE, ELF, and .NET file as well as shellcode snippets. We enrich
samples from the EMBER dataset with capability labels, and using these labels generate diferent types of
embeddings, including a Siamese embedding, which utilizes a contrastive loss over clusters of CAPA
attributes, as well as a novel ranking embedding, which uses the Spearman Rank Correlation Coeficient
as a loss and aims to embed ranked degree of similarity between diferent CAPA attribute clusters.
We then perform comparisons of these diferent metric embedding loss functions across two diferent
datasets: EMBER and SOREL-20M, on three diferent downstream transfer tasks: malware detection,
malware family classification and malware attribute classification, making comparisons to original
dataset benchmarks where applicable. Finally, we perform an analysis of adversarial robustness on the
three respective embedding types.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Background and Related Work</title>
      <p>
        Metric learning is a machine learning task that focuses on learning distances (i.e., metrics and/or
measures) between objects that captures some semantically meaningful notion of similarity. These
learned metric functions play an important role in fields including information retrieval, ranking,
and recommendation systems [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. The key property of a similarity metric/measure is that it maps
similar objects close together and dissimilar objects far apart within the learned metric space. In
practice, the objects are represented by a set of features, the metric function is the transformation of
the features into a common metric space, and the learning process finds a transformation such that the
similarity/dissimilarity behavior is correct with respect to the labels provided during training. Various
learning architectures have been proposed, including Siamese networks that learn from the distances
between pairs of objects, and triplet networks that use three samples to capture both similarity and
dissimilarity to an anchor [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ], [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ]. There are also diferent loss functions for each architecture along
with other subtle modifications of the learning process that can be applied to improve results (e.g.,
specialized algorithms for stochastic gradient descent [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]).
      </p>
      <p>
        The Spearman embedding technique that we introduce is not the first to incorporate ranking
information into a metric Embedding. The triplet based approach to learning was originally proposed as a
method to learn a function for object ranking [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ] and used an anchor  with a positive and negative pair
, and  respectively. This work has been extended and become popular in deep learning, with most
works focusing on the embedding constraints (e.g., L2 normalized or unconstrained) and the approach
for finding triplet pairs [
        <xref ref-type="bibr" rid="ref10 ref11 ref12 ref13 ref14 ref8 ref9">8, 9, 10, 11, 12, 13, 14</xref>
        ], however recent work has shown that most of these
gains may be attributed to learning algorithm improvements and model architecture (e.g., invention of
batch-norm), rather than improvements in the triplet learning procedure [15]. In contrast our work
comes full-circle, developing a ranking based loss based on the Spearman coeficient of correlation to
try and capture more fine-grained information than the standard triplet loss.
      </p>
      <p>To perform metric learning, we require a dataset of objects along with their similarities, which act as
labels in a supervised ML setting. Since our objects are binary portable executables (PEs) we need to
define a meaningful notion of similarity among binaries. Binary similarity gauges the likeness between
two binary files and can be defined in several diferent ways. Perhaps the cleanest definition is that two
binaries are similar if they were compiled from the same source code or contain a large fraction of the
same source code [16], [17]. This definition is particularly useful from a malware reverse engineering
standpoint: knowing that a file contains source code from a known piece of malware can significantly
speed up analysis. However, this definition introduces problems when labeling a dataset of binary
ifles built from unknown source code. More broadly, binary similarity can be defined as two files
whose structures are similar. This definition is the one often used by those developing fuzzy or locality
sensitive hashing algorithms [18, 19, 20, 21]. While less precise, these functions are computationally
easier to compute and some are amenable to fast (( log ) or faster) database lookups. These hashes
are routinely used in the malware analysis space, lacking any better option. Critically, recent work
where ground-truth (as assessed by manual reverse engineering) that hashes of this nature can produce
true-positive rates near 99.8%, at the cost of many false negatives [22, 23]. Given a sample , this allows
selecting a similar pair  with high confidence. Selecting a negative pair  can still be done with high
confidence by random selection, since only a minority of samples will be similar to any given .</p>
      <p>To the best of our knowledge, ours is the first work to pursue a discriminative style triplet loss as
our method of learning a general purpose feature representation. Prior methods generaly fall into
the category of being byte-based static processes or heavy lifting processes to extract higher level
code representations. In both cases, these methods are not amenable to being feature vectors that can
adjust to population change over time (i.e., quarterly retraining) in our deployment scenario (i.e., low
overhead).</p>
      <p>Prior byte-based and compression based approaches [24, 25] to constructing a feature vector have
been proposed, which allow for similarity search in a computationally eficient manner. Similarly digital
forensic hashes, which produce a hash-code of fixed or variable length that can be used to calculate
similarities [26, 27, 28, 29, 30, 31, 26, 32] are another approach that works on raw byte content. These
approaches are often fast and low-overhead. However, no learning step occurs for either of these types
of approaches, which prevents the method from being able to adapt to changes in the population of
malware.</p>
      <p>The other primary approach are code similarity measures. These tend to work at either the disassembly
[33, 34, 35] or disassembly call-graph [36, 37, 38], and use a neural network to train an auto-regressive
model thata can produce a fixed-length representation. This allows adapting the model over time, but the
reliance on at least disassembling the given executable limits our ability to deploy such representations.
Disassembly itself is computationally demanding, and often error-prone, as many times a file will not
yield accurate disassembly without unpacking or deobfuscation. These processes may need to be done
manually. Combined this makes the approach undesirable for our goals.</p>
    </sec>
    <sec id="sec-3">
      <title>3. Approach</title>
      <sec id="sec-3-1">
        <title>3.1. Overview</title>
        <p>In this paper, we focus on building a model that produces embeddings of Windows PE files. The goal
is to learn a representation that can be used for multiple downstream malware analysis tasks. The
methodology can be separated into two phases. Figure 1 represents the first phase where an embedding
model is trained. The starting point is the raw data, which in our case is the EMBER 2018 dataset [39], a
set of 1 million PE files seen in or before 2018. The raw data goes through two steps: (1) a featurization
step, and (2) a step to compute file information that aids in determining the pairwise similarity between
any two files. For featurization, we focus on subject matter expert (SME)-derived, static features that
are eficient to compute and which capture a broad range of malicious signals. These features include
things such as the APIs imported, parsing errors, entropy, and byte distributions.</p>
        <p>To determine pairwise similarity between two PE files, one can use a tool like CAPA [ 40] that detects
capabilities of executable files (i.e., two files with overlapping capabilities are similar). Notably, we
hypothesize that using more complex similarity information than what is available naturally in the
features (e.g., disassembly-based similarity vs. static features) will imbue the learned metric space with
additional information without the added overhead of the more complex analysis techniques. Once
the data and labels are defined, we specify an architecture for the embedding, which we instantiate
with a multi-layered neural network. An algorithm then takes those components as input and trains an
embedding model. The training algorithm can use a metric embedding network, e.g., a Siamese network
or a triplet loss network to learn the model parameters that efectively cause similar PE files to be near
one another in the embedding space.</p>
        <p>During the second phase, as shown in Figure 1, we measure the transferability of the embedding space
to various malware analysis tasks. Concretely, we embed our training data and use that representation
to train new models for each downstream task. By keeping the models used for the transfer process
constant and only varying our embedding process we can make precise measurements of the utility
of various similarity information, loss function, binary representation, or other parameters of our
embedding network. The following sections detail our modeling setup.</p>
      </sec>
      <sec id="sec-3-2">
        <title>3.2. Network architecture</title>
        <p>Our embedding neural network architecture is shown in Figure 3. The network takes as input
2381dimensional static features from [39]. The features are first normalized via standard scaling with
respect to mean and variance on the EMBER 2018 training set, then fed to an embedding network,
which is comprised of four dense layers of dimension 4,000, 1,024, 512, and 512. Each layer uses a
sigmoid activation. Between the layers we include both a BatchNorm and a Dropout layer with a
dropout probability of 10%. Following those layers is the final embedding layer using a linear activation
with specified output dimension; in our experiments, we utilize an output dimension of 32. During
training the network outputs are then optionally normalized and losses, which compare CAPA attribute
information are evaluated and minimized via backpropagation.</p>
      </sec>
      <sec id="sec-3-3">
        <title>3.3. Enriching Metric Embeddings with CAPA Labels</title>
        <p>The CAPA system detects various capabilities of a binary file based using both the static analysis and
disassembly of the file, and yields a set of capabilities for each file. These capabilities are categorical
and non-mutually exclusive and are labeled with short text snippets, e.g., “read file". We incorporate
these generated sets of capabilities to enrich our embeddings via two diferent loss functions, which we
apply both solo and in tandem (via summation) in our experiments.</p>
        <sec id="sec-3-3-1">
          <title>3.3.1. Contrastive Loss</title>
          <p>Contrastive loss is defined as:</p>
          <p>contrastive = true  + (1 − true ) max(margin − , 0)
where  is the distance between a pair of points,  is 1 if the pair contains similar objects or 0 if the
objects are dissimilar, and margin is the desired separation between dissimilar objects and is a tunable
hyperparameter. Equation 1 requires that samples either belong to the same group or not, meaning
that we cannot include more fine-grained similarity (e.g., these two samples are 75% similar), in the
loss function. Consequently, in this case we convert the CAPA detection sets into hard clusters with a
locality sensitive hash. Employing a MinHash with one band and 64 permutations, we compute a single
hash (cluster) for each binary file, where two files are similar if they lie in the same cluster (  = 1)
and diferent otherwise (  = 0).</p>
          <p>During our experiments we employ a contrastive loss with a margin of 10 based on the Euclidean
distance of the embeddings for each pair of samples in the batch. Note that we have tried a few tuning
experiments for the margin hyperparameter but did not see significant improvements over this default.
(1)</p>
        </sec>
        <sec id="sec-3-3-2">
          <title>3.3.2. Spearman Loss</title>
          <p>While our contrastive approach assesses similarity based on CAPA clusters, it coarsely embeds binaries
as “similar" or “not similar", when in reality some sets of CAPA labels are more similar than others.
To account for finer-grained similarities, we employ a novel approach based on the Spearman Rank
Correlation Coeficient.</p>
          <p>Specifically, advances in approximate diferentiable sorting and ranking [ 41] allow us to optimize
Spearman’s rank correlation coeficient with stochastic gradient descent. This allows us to compute the
loss between a ground truth ranking and a predicted ranking from our model. This is desirable as it
allows inserting more nuanced information into the loss function based on finer grained degree , rather
than a simple binary similar/dissimilar decision. In our experiments the ranking is based on similarity,
from most similar to least. Given integer ranks we can define Spearman’s rank correlation coeficient as
 = 1 − 6 ∑︀(() − ())2 (2)</p>
          <p>(2 − 1)
where  and  are the ground truth similarity and predicted similarity of data point  and () and
() are the corresponding ranks. We assess ground truth similarity between two CAPA capability
sets as their Jaccard similarity, and use the soft rank implementation from [41] to compare predicted and
ground truth ranks. For a given batch, we use these ranks to establish the Spearman rank correlation
coeficient – the loss for that batch.</p>
        </sec>
      </sec>
      <sec id="sec-3-4">
        <title>3.4. Training Process</title>
        <p>All the layers of our networks are initialized by the Xavier algorithm [42] and trained with stochastic
gradient descent (SGD) to a maximum of 30 epochs with a learning rate of 0.001. The batching algorithm
used for SGD training was modified to better support our metric learning loss functions. Ordinarily,
each batch contains  randomly sampled (with replacement) clusters and  randomly sampled PE
ifles from each cluster (again, sampled with replacement). For our binary similarity problem, we are
confronted with two complications. First, each cluster can potentially contain both goodware and
malware unlike typical metric learning problems where clusters are homogeneous. Second, we have
an extremely large number of clusters ((105)). To address the goodware and malware heterogeneity
concern, we split each cluster  into two clusters, -goodware and -malware. When we sample 
clusters, we do so from the combination of all -goodware and -malware clusters. To address the
second concern, we sample  clusters without replacement and define the end of the epoch when the
model has processed examples from every cluster. This algorithm ensures we cover the full space of
goodware, malware, and clusters in each epoch while maintaining a balance between positive and
negative pairs in each batch. For these experiments, we set  = 20 and  = 4.</p>
      </sec>
      <sec id="sec-3-5">
        <title>3.5. Transfer Process</title>
        <p>After training the embedding, we measure the embedding’s usability on various malware classification
tasks. For our experiments, we train an embedding network using the EMBER 2018 training partition
and extracted CAPA labels. Once we have a trained embedding network, we can use this to extract
embeddings from any dataset with EMBER features. Using extracted embeddings for a given dataset, we
can then fit a lightweight classifier over the embeddings and corresponding labels to make predictions
for arbitrary diferent tasks.</p>
        <p>The choice of the best final classifier for each task is not obvious. Typically, generalization-based
learning using ensemble methods (e.g., random forests or gradient boosted trees) provide state of the
art performance on malware tasks. However, our feature space is unique in that distances between two
training points have meaning and decision tree methods that rely on splitting individual features may
have dificulty capturing that geometry. Notably, SVMs are a generalization-based method that could
take our metric space into account, but we ignore it here due to the computational cost of training
an SVM on very large datasets. An alternative would be an instance-based learning algorithm (e.g.,
-nearest neighbors), which explicitly considers distances between training data points. As we will
show in the following evaluation, we consider both instance and generalization-based classifiers, and
the best classifier can vary based on the transfer task.</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. Experiments</title>
      <sec id="sec-4-1">
        <title>4.1. Embedding Networks</title>
        <p>We trained various embedding networks using EMBER feature vectors and CAPA labeling extracted
from PEs in the EMBER 2018 train partition. These consist of:
• Contrastive loss on CAPA clusters.
• Spearman loss on Jaccard similarities between CAPA attribute sets.
• Mixed objective Spearman and Contrastive loss, where the net loss term is the sum of the losses.</p>
        <p>In practice, we employ a weighting of 10X on the Spearman loss term to bring the contributions
from each constituent loss term to roughly the same order of magnitude.</p>
        <p>We trained each embedding network according to the procedure discussed in Section 3.4. Since deep
learning models are not amenable to convex optimization (i.e., no global minimum guarantee), we
trained five diferent instantiations of each model in order to assess variance in performance. When
performing transfer task experiments, we then aggregated mean and standard deviation statistics across
embeddings from all five networks of a given type.</p>
      </sec>
      <sec id="sec-4-2">
        <title>4.2. Transfer Experiments on EMBER</title>
        <p>As an initial evaluation of our embeddings, we performed two transfer tasks on the EMBER dataset:
malware detection and malware family classification.</p>
        <p>(a) Goodware/Malware
(b) Malware Family</p>
        <p>The malware detection transfer task aims to detect malware by fitting a transfer classifier on
embeddings of the EMBER dataset along with malicious/benign labels. For this task, we extracted embeddings
across both train and test partitions of EMBER 2018. We then fit a lightGBM ensemble with 1000 trees
and otherwise default parameters over the embeddings extracted from the training set, and evaluated
using embeddings extracted from the test set. The results of this experiment are shown in Figure 6a in
terms of the area under the ROC curve (AU-ROC) on the test set.</p>
        <p>In this experimental setting, we tried diferent weightings of the mixed objective loss, with the
Spearman component both unweighted and up-weighted by a factor of 10 to be on the same scale as
the contrastive component. We notice that the transfer performance on the contrastive loss embedding
significantly outperforms the transfer performance on the Spearman loss embedding. However, both
embeddings which use a combination of the two losses ofer better classification performance than
strictly either of the embeddings trained on a solo loss (Spearman or Contrastive), with the weighted
mixed objective loss outperforming the unweighted. Note that none of the transfer malicious/benign
classifiers on EMBER 2018 perform comparably to the baseline model from [39].</p>
        <p>The second transfer task is a malware family recognition task, which utilizes a nearest neighbor
classifier in the embedding space in conjunction with the EMBER 2018 malware family labels (derived
via AVClass [43]) to attribute malware family, for only the malicious samples. These results are shown
in Figure 6b. While here the performance evaluation is in terms of accuracy not AU-ROC, we notice the
same performance trend across embedding types as for the detection transfer task.</p>
      </sec>
      <sec id="sec-4-3">
        <title>4.3. Transfer Experiments on SOREL-20M</title>
        <p>We additionally evaluated the performance of our embeddings for diferent tasks on the SOREL-20M
dataset. SOREL is a large industry-scale dataset with publicly available labeling telemetry beyond
just malicious/benign detection; it also contains public labeling telemetry for 11 distinct malware
attributes, namely: Adware, Crypto Miner, Downloader, Dropper, File Infector, Flooder, Installer, Packed,
Ransomware, Spyware, and Worm. Note that these attributes are non-mutually exclusive across samples,
meaning that a given malware sample can have multiple malware attributes.</p>
        <p>SOREL also contains diferent data with a diferent data distribution than EMBER (on which the
embeddings were extracted). This suggests any strong performance over the EMBER-to-SOREL transition
is a indication of the robustness of our approach to producing general purpose features for downstream
tasks.</p>
        <p>We extracted 32-dimensional embeddings for all of the SOREL samples apriori, and trained
secondstage task-specific lightGBM classifiers on the extracted embeddings. We assessed embedding
performance/quality for two distinct tasks: malware detection and malware attribute labeling.</p>
        <p>Results from the malware detection task are shown in Figure 7. Embedding extraction and lightGBM
ift was performed five diferent times to obtain error bars. Consistent with our transfer experiments on
EMBER, the mixed objective weighted Spearman+Contrastive embedding yields the highest AU-ROC,
slightly outperforming the Contrastive embedding and significantly outperforming the Spearman
embedding. For reference, the lightGBM baseline trained on full 2381-dimensional features has an AU-ROC
of 0.981 ± 0.002 [44], a relative average improvement over the top-performing Spearman+Contrastive
model of 0.05%. However, storing the full 2381-dimensional feature vectors requires 74.4 times the
amount of storage of as that of the 32-dimensional embeddings, indicating that in practice, the
topperforming embeddings significantly reduce the storage burden at a slight reduction in net performance.</p>
        <p>Results from the malware attribute labeling task are shown in Table 1. For this task, we fit lightGBM
classifiers across each of the malware tags, using 1-hit for each tag as a criterion for presence of the
attribute, consistent with [44]. Notably, we see a similar pattern with the Mixed-10 loss on average
outperforming the Contrastive loss and both losses on average, outperforming the Spearman loss.
Note also, that the Mixed-10 loss under-performs the Contrastive loss where Spearman performs
poorly. On average, the results for tagging under-perform the baseline provided with SOREL-20M
benchmark, though this is a somewhat invalid comparison, as the attribute baselines from [44] utilized
a large multi-target network, factoring in number of vendor hits, malicious/benign classification, and
simultaneous attribute predictions; thus some of the performance discrepancy is likely due to limitations
of single-target classifiers.</p>
        <p>Adware
Crypto Miner
Downloader</p>
        <p>Dropper
File Infector</p>
        <p>Flooder
Installer</p>
        <p>Packed
Ransomware</p>
        <p>Spyware</p>
        <p>Worm</p>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>5. Discussion</title>
      <p>We have introduced two diferent approaches to enrich metric embeddings with static disassembly
capabilities information and performed evaluations thereof on multiple downstream tasks. These
approaches consist of a fine-grained Spearman embedding approach and a coarse-grained Contrastive
embedding approach. In the vast majority of our experiments, the coarse-grained Contrastive approach
exhibited superior performance to the finer-grained Spearman approach. In some respects, this is not
surprising, as Contrastive loss inherently forces separability in a way that the Spearman loss does not.
An in-depth examination of similarity distributions and adoption of additional similarity measures
other than Jaccard similarity could be helpful in improving the Spearman embedding. Consistent with
other literature in the ML security/applied ML space, we found that combining both Spearman and
Contrastive embedding losses generally improved performance as did balancing loss contributions to a
similar order of magnitude [45, 46, 47].</p>
      <p>While our embeddings performed comparably to classifiers trained on raw features for certain tasks,
they did not work so well for others. Among a variety of factors, this may be due to including semantic
information inherent to the CAPA embeddings, over/under-fitting, and hyperparameter selection, all of
which are logical areas of follow-up research. Generally, we surmise that improving performance of
metric embeddings for additional tasks is trivially feasible by utilizing additional training objectives.
These may include malicious/benign labels, malware attribute tags, MITRE ATT&amp;CK tactics (notably,
CAPA outputs these as well as attributes) and additional metadata. Moreover, examining how embedding
performance scales when training on larger more heterogeneous groups of samples and evaluating on
substantially concept-drifted data could ofer further insight into embedding performance and design
(e.g., [48]).</p>
      <p>Notably, a low-dimensional embedding which performs well for a variety of classification and/or
information retrieval tasks could yield significant computational and storage savings over utilizing raw
features or binaries. Such embeddings could be utilized in both academic contexts, where compute
resources are often limited or in commercial contexts for rapid prototyping. As a reference, the
SOREL20M dataset is an order of magnitude smaller than industry datasets which are typically used to
train commercial PE malware detectors, yet it still comes with a warning about potentially incurring
bandwidth fees or exhausting disk space. Even in featurized format as 32-bit floating point, the
SOREL20M dataset requires 172 GB of storage. Using the embeddings introduced in this paper, this can be
compressed to roughly 2.3 GB, which is small enough to fit in memory, even for most laptops.
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