Data Mining Techniques for Malware Detection

 

R. K. Agrawal School of Computer and Systems Sciences

Jawaharlal Nehru UniversityNewDelhi-110067

 1

Outline• Data Mining• Classification • Clustering• Association Rules• Experimental Results• Conclusion and Future Work 2

Motivation: “Necessity is the Mother of

Invention• Data explosion problem

– Automated data collection tools lead to tremendous amounts of data stored in databases and other information repositories

• We are drowning in data, but starving for knowledge! • Solution: data mining

– Extraction of interesting knowledge (rules, regularities, patterns, constraints) from data in large databases

3

Commercial Viewpoint

• Lots of data is being collected and warehoused – Web data, e-commerce– purchases at department/

grocery stores– Bank/Credit Card

transactions

• Computers have become cheaper and more powerful

• Competitive Pressure is Strong – Provide better, customized services for an edge (e.g. in

Customer Relationship Management) 4

Scientific Viewpoint

• Data collected and stored at enormous speeds (GB/hour)– remote sensors on a satellite– Network related Log files– microarrays generating gene

expression data– scientific simulations

generating terabytes of data• Traditional techniques infeasible for

raw data• Data mining may help scientists

– in classifying and segmenting data– in Hypothesis Formation

5

What Is Data Mining?

• Data mining (knowledge discovery in databases):– Extraction of interesting (non-trivial, implicit,

previously unknown and potentially useful) information or patterns from data in large databases

• Alternative names:– Knowledge discovery(mining) in databases (KDD),

knowledge extraction, data/pattern analysis, data archeology, business intelligence, etc.

6

Data Mining Tasks

• Prediction Tasks– Use some variables to predict unknown or future values of

other variables• Description Tasks

– Find human-interpretable patterns that describe the data.

Common data mining tasks– Classification [Predictive]– Clustering [Descriptive]– Association Rule Discovery [Descriptive]– Sequential Pattern Discovery [Descriptive]– Regression [Predictive]– Deviation Detection [Predictive]

7

Classification: Definition

• Given a collection of records (training set )– Each record contains a set of attributes, one of the

attributes is the class label.

• Find a model for class attribute as a function of the values of other attributes.

• Goal: previously unseen records should be assigned a class as accurately as possible.

YX :q

8

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Classification—A Two-Step Process

• Model construction: describing a set of predetermined classes– Each tuple/sample is assumed to belong to a predefined

class, as determined by the class label attribute– The set of tuples used for model construction is training

set– The model is represented as classification rules, decision

trees, or mathematical formulae

• Model usage: for classifying future or unknown objects– Estimate accuracy of the model

• The known label of test sample is compared with the classified result from the model

• Accuracy rate is the percentage of test set samples that are correctly classified by the model

– If the accuracy is acceptable, use the model to classify data tuples whose class labels are not known

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Process (1): Model Construction

TrainingData

NAME RANK YEARS TENUREDRahul Assistant Prof 3 noMohan Assistant Prof 7 yesDev Professor 2 yesKirti Associate Prof 7 yesSudhir Assistant Prof 6 noArun Associate Prof 3 no

ClassificationAlgorithms

IF rank = ‘professor’OR years > 6THEN tenured = ‘yes’

Classifier(Model)

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Process (2): Using the Model in Prediction

Classifier

TestingData

NAME RANK YEARS TENUREDTarun Assistant Prof 2 noManish Associate Prof 7 noJolly Professor 5 yesHarsh Assistant Prof 7 yes

Unseen Data

(Jolly Professor, 5)

Tenured?

Classification: Application

• Malware Detection– Goal: Predict whether the given binary is

Malware or not.– Approach:

• Use both kind of binaries (Normal and Malware)• Learn a model for the class of the binaries.• Use this model to detect malware by observing a

binary.

12

Clustering Definition

• Given a set of data points, each having a set of attributes, and a similarity measure among them, find clusters such that– Data points in one cluster are more similar to

one another.– Data points in separate clusters are less similar

to one another.• Similarity Measures:

– Euclidean Distance if attributes are continuous.– Other Problem-specific Measures.

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Illustrating Clustering

Euclidean Distance Based Clustering in 3-D space.

Intracluster distancesare minimized

Intercluster distancesare maximized

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Clustering: Application

• Binaries Segmentation:– Goal: subdivide a given set of binaries into

distinct subsets of binaries

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Association Rule Discovery: Definition

• Given a set of records each of which contain some number of items from a given collection;– Produce dependency rules which will predict occurrence

of an item based on occurrences of other items.

TID Items

1 Bread, Coke, Milk2 Beer, Bread3 Beer, Coke, Diaper, Milk4 Beer, Bread, Diaper, Milk5 Coke, Diaper, Milk

Rules Discovered: {Bread} --> {Milk} {Diaper} --> {Beer}

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The Sad Truth About Diapers and Beer

• So, don’t be surprised if you find six-packs stacked next to diapers!

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Association Rule Discovery: Application

• Malware Rules– Goal: To identify activities that are happen

together in a given malware.

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Sequential Pattern Discovery: Definition

Given is a set of objects, with each object associated with its own timeline of events, find rules that predict strong sequential dependencies among different events:

– In telecommunications alarm logs, • (Inverter_Problem Excessive_Line_Current) (Rectifier_Alarm) --> (Fire_Alarm)

– In point-of-sale transaction sequences,• Computer Bookstore:

(Intro_To_Visual_C) (C++_Primer) --> (Perl_for_dummies)• Athletic Apparel Store:

(Shoes) (Racket, Racketball) --> (Sports_Jacket)

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Classification Example

x

2

1

xx

height

weight2X

Training examples

)},(,),,{( 11 ll yy xx

1x

2x

Jy

Hy Linear classifier:

0)(0)(

)q(bifJbifH

xwxw

x0)( bxw

20

Classification Techniques

• Decision Trees• Naïve Bayes• Support Vector Machines• Neural Networks• Parzen Window• K-nearest neigbor

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Issues: Data Preparation

• Data cleaning– Preprocess data in order to reduce noise and

handle missing values• Relevance analysis (feature selection)

– Remove the irrelevant or redundant attributes• Data transformation

– Generalize and/or normalize data

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Issues: Evaluating Classification Methods

• Accuracy– classifier accuracy: predicting class label– predictor accuracy: guessing value of predicted

attributes• Speed

– time to construct the model (training time)– time to use the model (classification/prediction time)

• Robustness: handling noise and missing values• Scalability: efficiency in disk-resident databases • Interpretability

– understanding and insight provided by the model• Other measures, e.g., goodness of rules, such as

decision tree size or compactness of classification rules

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Decision Tree Induction: Training Dataset

age income student credit_rating buys_computer<=30 high no fair no<=30 high no excellent no31…40 high no fair yes>40 medium no fair yes>40 low yes fair yes>40 low yes excellent no31…40 low yes excellent yes<=30 medium no fair no<=30 low yes fair yes>40 medium yes fair yes<=30 medium yes excellent yes31…40 medium no excellent yes31…40 high yes fair yes>40 medium no excellent no

This follows an example of Quinlan’s ID3

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A Decision Tree for “buys_computer”

age?

overcast

student? credit rating?

<=30 >40

no yes yes

yes

31..40

no

fairexcellentyesno

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Algorithm for Decision Tree Induction

• Basic algorithm (a greedy algorithm)– Tree is constructed in a top-down recursive divide-and-

conquer manner– At start, all the training examples are at the root– Attributes are categorical (if continuous-valued, they are

discretized in advance)– Examples are partitioned recursively based on selected

attributes– Test attributes are selected on the basis of a heuristic or

statistical measure (e.g., information gain)• Conditions for stopping partitioning

– All samples for a given node belong to the same class– There are no remaining attributes for further partitioning –

majority voting is employed for classifying the leaf– There are no samples left

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Attribute Selection Measure: Information Gain (ID3/C4.5)

Select the attribute with the highest information gain

Let pi be the probability that an arbitrary tuple in D belongs to class Ci, estimated by |Ci, D|/|D|

Expected information (entropy) needed to classify a tuple in D:

Information needed (after using A to split D into v partitions) to classify D:

Information gained by branching on attribute A

)(log)( 21

i

m

ii ppDInfo

)(||||

)(1

j

v

j

jA DI

DD

DInfo

(D)InfoInfo(D)Gain(A) A

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Attribute Selection: Information Gain Class P: buys_computer =

“yes” Class N: buys_computer =

“no”

means “age <=30” has 5 out of 14 samples, with 2 yes’es and 3 no’s. Hence

Similarly,

age pi ni I(pi, ni)<=30 2 3 0.97131…40 4 0 0>40 3 2 0.971

694.0)2,3(145

)0,4(144)3,2(

145)(

I

IIDInfoage

048.0)_(151.0)(029.0)(

ratingcreditGainstudentGainincomeGain

246.0)()()( DInfoDInfoageGain ageage income student credit_rating buys_computer<=30 high no fair no<=30 high no excellent no31…40 high no fair yes>40 medium no fair yes>40 low yes fair yes>40 low yes excellent no31…40 low yes excellent yes<=30 medium no fair no<=30 low yes fair yes>40 medium yes fair yes<=30 medium yes excellent yes31…40 medium no excellent yes31…40 high yes fair yes>40 medium no excellent no

)3,2(145 I

940.0)145(log

145)

149(log

149)5,9()( 22 IDInfo

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Computing Information-Gain for Continuous-Value Attributes

• Let attribute A be a continuous-valued attribute• Must determine the best split point for A

– Sort the value A in increasing order– Typically, the midpoint between each pair of adjacent

values is considered as a possible split point• (ai+ai+1)/2 is the midpoint between the values of ai and ai+1

– The point with the minimum expected information requirement for A is selected as the split-point for A

• Split:– D1 is the set of tuples in D satisfying A ≤ split-point,

and D2 is the set of tuples in D satisfying A > split-point

Linear Classifiers

denotes +1denotes -1

f(x,w,b) = sign(w x + b)

Any of these would be fine..

..but which is best?

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Support Vector Machine

What we know:• w . x+ + b = +1 • w . x- + b = -1 • w . (x+-x-) = 2

“Predict Class = +1”

zone

“Predict Class = -1”

zonewx+b=1

wx+b=0wx+b=-1

X-

x+

wwwxxM 2)(

M=Margin Width Support

Vectors are those datapoints that the margin pushes up against

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Linear SVM Mathematically• Goal: 1) Correctly classify all training data if yi = +1

If yi = -1 for all i

2) Maximize the Margin

same as minimize

• We can formulate a Quadratic Optimization Problem and solve for w and b

Minimize

subject to

wM 2

www t

21)(

1bwxi1bwxi

1)( bwxy ii

1)( bwxy ii

i

wwt

21

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Linear SVM. Cont.

• Requiring the derivatives with respect to w,b to vanish yields:

• KKT conditions yield:

• Where:

i

xx

i

m

ii

m

i

m

jji

m

ii

0

0y:toSubject

,yy21maximize

1

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1 1

jiji

1

iii xwybanyfor ,,0

m

i

iii xyw

1

33

Linear SVM. Cont.• The resulting separating function is:

bxxyxfm

i

iii

1

,sgnsgn

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Linear SVM. Cont.

• Requiring the derivatives with respect to w,b to vanish yields:

• KKT conditions yield:

• Where:

i

xx

i

m

ii

m

i

m

jji

m

ii

0

0y:toSubject

,yy21maximize

1

i

1 1

jiji

1

iii xwybanyfor ,,0

m

i

iii xyw

1

35

Linear SVM. Cont.• The resulting separating function is:

• Notes:– The points with α=0 do not affect the solution.– The points with α≠0 are called support vectors.– The equality conditions hold true only for the Support

Vectors.

bxxyxfm

i

iii

1

,sgnsgn

36

Non-separable case• The modifications yield the following problem:

iC

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ii

m

i

m

jji

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0

0y:toSubject

,yy21maximize

1

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1

37

Non Linear SVM

• Note that the training data appears in the solution only in inner products.

• If we pre-map the data into a higher and sparser space we can get more separability and a stronger separation family of functions.

• The pre-mapping might make the problem infeasible.

• We want to avoid pre-mapping and still have the same separation ability.

• Suppose we have a simple function that operates on two training points and implements an inner product of their pre-mappings, then we achieve better separation with no added cost.

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Non-linear SVMs: Feature spaces

• General idea: the original feature space can always be mapped to some higher-dimensional feature space where the training set is separable:

Φ: x → φ(x)

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The “Kernel Trick”

• The linear classifier relies on inner product between vectors K(xi,xj)=xiTxj

• If every datapoint is mapped into high-dimensional space via some transformation Φ: x → φ(x), the inner product becomes:

K(xi,xj)= φ(xi) Tφ(xj)

• A kernel function is a function that is equivalent to an inner product in some feature space.

• Example: 2-dimensional vectors x=[x1 x2]; let K(xi,xj)=(1 + xi

Txj)2,

Need to show that K(xi,xj)= φ(xi) Tφ(xj):

K(xi,xj)=(1 + xiTxj)2

,= 1+ xi12xj1

2 + 2 xi1xj1 xi2xj2+ xi2

2xj22 + 2xi1xj1 + 2xi2xj2=

= [1 xi12 √2 xi1xi2 xi2

2 √2xi1 √2xi2]T [1 xj12 √2 xj1xj2 xj2

2 √2xj1 √2xj2] = = φ(xi)

Tφ(xj), where φ(x) = [1 x12 √2 x1x2 x2

2 √2x1 √2x2]• Thus, a kernel function implicitly maps data to a high-dimensional space

(without the need to compute each φ(x) explicitly).

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Mercer Kernels

• A Mercer kernel is a function:

for which there exists a function:

such that:

• A function k(.,.) is a Mercer kernel if for any function g(.), such that:

the following holds true:

dxxg )(2

0),()()( dxdyyxkygxg

RXXk dd :

HX d :

)(),(),(, yxyxkXyx d

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Commonly used Mercer Kernels

• Homogeneous Polynomial Kernels:

• Non-homogeneous Polynomial Kernels:

• Radial Basis Function (RBF) Kernels:

pyxyxk 1,),(

2exp),( yxyxk

pyxyxk ,),(

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Solution of non-linear SVM• The problem:

• The separating function:

iC

xxk

i

m

ii

m

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jji

m

ii

0

0y:toSubject

,yy21maximize

1

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1

bxxkyxfm

i

iii

1

,sgnsgn

43

Multi-Class SVM

• Approaches:

• One against One ( K (K-1) / 2 ) binary Classifiers requiredOutputs of the classifiers are aggregated to make the final decision.

• One against All (K binary Classifiers required): It trains k binary classifiers, each of which separates one class from the other (k-1) classes. Given a data point X , the binary classifier with the largest output determines the class of X.

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Why Is SVM Effective on High Dimensional Data?

The complexity of trained classifier is characterized by the # of support vectors rather than the dimensionality of the data

The support vectors are the essential or critical training examples —they lie closest to the decision boundary (MMH)

If all other training examples are removed and the training is repeated, the same separating hyperplane would be found

The number of support vectors found can be used to compute an (upper) bound on the expected error rate of the SVM classifier, which is independent of the data dimensionality

Thus, an SVM with a small number of support vectors can have good generalization, even when the dimensionality of the data is high

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Experiments

• Source of data: Preprocessed data in terms of API Calls taken from data collected from C-Dac Mohali.

• Description of data

Sample Space

Training set

Testing set

Benign 534 50 484Malicious 168 50 118Total 702 100 602

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Classifier Accuracy Measures

• Performance measuressensitivity = t-pos/pos /* true positive recognition rate */specificity = t-neg/neg /* true negative recognition rate

*/

accuracy = sensitivity * pos/(pos + neg) + specificity * neg/(pos + neg)

C1 C2

C1 True positive False negative

C2 False positive

True negative

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Experimental Results

Classifier sensitivity specificity

k=5 K=6 K=7 K=5 K=6 K=7C4.5 70.86 71.23 69.68 68.62 69.96 61.05

SVM 75.26 76.79 75.18 73.54 78.34 74.46

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Observations

• The performance of SVM classifier is significantly better in comparison to C4.5.

• The performance is dependent on the size of feature size

• SVM requires less training samples in comparison C4.5. Hence, svm is a better choice as collecting malicious samples is difficult.

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Conclusion & Future Work

• SVM is a better classification technique which can be used for detection of Malware.

• Needs attention to construct better feature representation for better generalization

• How to extend it to multi-class malware problem

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References• C. J. C. Burges. A Tutorial on Support Vector Machines for Pattern

Recognition. Data Mining and Knowledge Discovery, 2(2): 121-168, 1998. • J. R. Quinlan. C4.5: Programs for Machine Learning. Morgan Kaufmann, 1993.• P. Tan, M. Steinbach, and V. Kumar. Introduction to Data Mining. Addison

Wesley, 2005.• I. H. Witten and E. Frank. Data Mining: Practical Machine Learning Tools and

Techniques, 2ed. Morgan Kaufmann, 2005.• Han and Kamber, Data Mining Concepts• B. Zhang, J. Yin, J. Hao, D. Zhang, S. Wang, Using Support Vector Machine to detect

unknown computer viruses, Int. Journal of Computational Intelligence Research, vol. 2, No. 1, pp. 100-104, 2006.

• Szappanos,G.: Are There Any Polymorphic Macro Viruses at ALL (and What to Do with Them).in Proceedings of the 12th International Virus Bulletin Conference, 2001.

• Forrest,S., Hofmeyr, S. A., Somayaji, A.: Computer immunology. Communications of the ACM. 10, pp. 88–96, 1997.

• Lee,W., Dong,X.: Information-Theoretic measures for anomaly detection. In: Needham,R., Abadi M, (eds):. Proceedings of the 2001 IEEE Symposium on Security and Privacy Oakland, CA: IEEE Computer Society Press, pp. 130-143, 2001.

• LIBSVM. http://www.csie.ntu.edu.tw/~cjlin/.

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