Machine Learning for Fraud Detection in Streaming Services

Introduction

Streaming services serve content to millions of users all over the world. These services allow users to stream or download content across a broad category of devices including mobile phones, laptops, and televisions. However, some restrictions are in place, such as the number of active devices, the number of streams, and the number of downloaded titles. Many users across many platforms make for a uniquely large attack surface that includes content fraud, account fraud, and abuse of terms of service. Detection of fraud and abuse at scale and in real-time is highly challenging.

Background on Anomaly Detection

Anomalies (also known as outliers) are defined as certain patterns (or incidents) in a set of data samples that do not conform to an agreed-upon notion of normal behavior in a given context.

Figure 1. Schematic of a streaming service platform: (a) illustrates device types that can be used for streaming, (b) designates the set of authentication and authorization systems such as license and manifest servers for providing encrypted contents as well as decryption keys and manifests, and (c) shows the streaming service provider, as a surrogate entity for digital content providers, that interacts with the other two components.

Streaming Platforms

Commercial streaming platforms shown in Figure 1 mainly rely on Digital Rights Management (DRM) systems. DRM is a collection of access control technologies that are used for protecting the copyrights of digital media such as movies and music tracks. DRM helps the owners of digital products prevent illegal access, modification, and distribution of their copyrighted work. DRM systems provide continuous content protection against unauthorized actions on digital content and restrict it to streaming and in-time consumption. The backbone of DRM is the use of digital licenses, which specify a set of usage rights for the digital content and contain the permissions from the owner to stream the content via an on-demand streaming service.

Data

Data Labeling

For the task of anomaly detection in streaming platforms, as we have neither an already trained model nor any labeled data samples, we use structural a priori domain-specific rule-based assumptions, for data labeling. Accordingly, we define a set of rule-based heuristics used for identifying anomalous streaming behaviors of clients and label them as anomalous or benign. The fraud categories that we consider in this work are (i) content fraud, (ii) service fraud, and (iii) account fraud. With the help of security experts, we have designed and developed heuristic functions in order to discover a wide range of suspicious behaviors. We then use such heuristic functions for automatically labeling the data samples. In order to label a set of benign (non-anomalous) accounts a group of vetted users that are highly trusted to be free of any forms of fraud is used.

  • (i) Rapid license acquisition: a heuristic that is based on the fact that benign users usually watch one content at a time and it takes a while for them to move on to another content resulting in a relatively low rate of license acquisition. Based on this reasoning, we tag all the accounts that acquire licenses very quickly as anomalous.
  • (ii) Too many failed attempts at streaming: a heuristic that relies on the fact that most devices stream without errors while a device, in trial and error mode, in order to find the “right’’ parameters leaves a long trail of errors behind. Abnormally high levels of errors are an indicator of a fraud attempt.
  • (iii) Unusual combinations of device types and DRMs: a heuristic that is based on the fact that a device type (e.g., a browser) is normally matched with a certain DRM system (e.g., Widevine). Unusual combinations could be a sign of compromised devices that attempt to bypass security enforcements.
Table 1. The list of streaming related features with the suffixes pct and cnt respectively referring to percentage and count

Data Statistics

In this part, we present the statistics of the features presented in Table 1. Over 30 days, we have gathered 1,030,005 benign and 28,045 anomalous accounts. The anomalous accounts have been identified (labeled) using the heuristic-aware approach. Figure 2(a) shows the number of anomalous samples as a function of fraud categories with 8,741 (31%), 13,299 (47%), 6,005 (21%) data samples being tagged as content fraud, service fraud, and account fraud, respectively. Figure 2(b) shows that out of 28,045 data samples being tagged as anomalous by the heuristic functions, 23,838 (85%), 3,365 (12%), and 842 (3%) are respectively considered as incidents of one, two, and three fraud categories.

Figure 2. Number of anomalous samples as a function of (a) fraud categories and (b) number of tagged categories.
Figure 3. Correlation matrix of the features presented in Table 1 for (a) clean and (b) anomalous data samples.

Label Imbalance Treatment

It is well known that class imbalance can compromise the accuracy and robustness of the classification models. Accordingly, in this work, we use the Synthetic Minority Over-sampling Technique (SMOTE) to over-sample the minority classes by creating a set of synthetic samples.

Figure 4. Synthetic Minority Over-sampling Technique

Evaluation Metrics

For evaluating the performance of the anomaly detection models we consider a set of evaluation metrics and report their values. For the one-class as well as binary anomaly detection task, such metrics are accuracy, precision, recall, f0.5, f1, and f2 scores, and area under the curve of the receiver operating characteristic (ROC AUC). For the multi-class multi-label task we consider accuracy, precision, recall, f0.5, f1, and f2 scores together with a set of additional metrics, namely, exact match ratio (EMR) score, Hamming loss, and Hamming score.

Model Based Anomaly Detection

In this section, we briefly describe the modeling approaches that are used in this work for anomaly detection. We consider two model-based anomaly detection approaches, namely, (i) semi-supervised, and (ii) supervised as presented in Figure 5.

Figure 5. Model-based anomaly detection approaches: (a) semi-supervised and (b) supervised.

Semi-Supervised Anomaly Detection

The key point about the semi-supervised model is that at the training step the model is supposed to learn the distribution of the benign data samples so that at the inference time it would be able to distinguish between the benign samples (that has been trained on) and the anomalous samples (that has not observed). Then at the inference stage, the anomalous samples would simply be those that fall out of the distribution of the benign samples. The performance of One-Class methods could become sub-optimal when dealing with complex and high-dimensional datasets. However, supported by the literature, deep neural autoencoders can perform better than One-Class methods on complex and high-dimensional anomaly detection tasks.

Supervised Anomaly Detection

Binary Classification: In the anomaly detection task using binary classification, we only consider two classes of samples namely benign and anomalous and we do not make distinctions between the types of the anomalous samples, i.e., the three fraud categories. For the binary classification task we use multiple supervised classification approaches, namely, (i) Support Vector Classification (SVC), (ii) K-Nearest Neighbors classification, (iii) Decision Tree classification, (iv) Random Forest classification, (v) Gradient Boosting, (vi) AdaBoost, (vii) Nearest Centroid classification (viii) Quadratic Discriminant Analysis (QDA) classification (ix) Gaussian Naive Bayes classification (x) Gaussian Process Classifier (xi) Label Propagation classification (xii) XGBoost. Finally, upon doing stratified k-fold cross-validation, we carry out an efficient grid search to tune the hyper-parameters in each of the aforementioned models for the binary classification task and only report the performance metrics for the optimally tuned hyper-parameters.

Results and Discussion

Table 2 shows the values of the evaluation metrics for the semi-supervised anomaly detection methods. As we see from Table 2, the deep auto-encoder model performs the best among the semi-supervised anomaly detection approaches with an accuracy of around 96% and f1 score of 94%. Figure 6(a) shows the distribution of the Mean Squared Error (MSE) values for the anomalous and benign samples at the inference stage.

Table 2. The values of the evaluation metrics for a set of semi-supervised anomaly detection models.
Figure 6. For the deep auto-encoder model: (a) distribution of the Mean Squared Error (MSE) values for anomalous and benign samples at the inference stage — (b) confusion matrix across benign and anomalous samples- (c) Mean Squared Error (MSE) values averaged across the anomalous and benign samples for each of the 23 features.
Table 3. The values of the evaluation metrics for a set of supervised binary anomaly detection classifiers.
Table 4. The values of the evaluation metrics for a set of supervised multi-class multi-label anomaly detection approaches. The values in parenthesis refer to the performance of the models trained on the original (not upsampled) dataset.
Figure 7. The normalized feature importance values (NFIV) for the multi-class multi-label anomaly detection task using the XGBoost approach in Table 4 across the three anomaly classes, i.e., (a) content fraud, (b) service fraud, and (c) account fraud.

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