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Technical Report TR740:
Insider Threat Event Detection in User-System Interactions

Pablo Moriano, Jared Pendleton, Steven Rich, and L. Jean Camp
(Sep 2017), 12
[A final version of this paper was published in Proceedings of MIST'17, October 30, 2017, https://doi.org/10.1145/3139923.3139928.]
Abstract:
Detection of insider threats relies on monitoring individuals and their interactions with organizational resources. Identification of anomalous insiders typically relies on supervised learning models that use labeled data. However, such labeled data is not easily obtainable. The labeled data that does exist is also limited by current insider threat detection methods and undetected insiders would not be included. These models also inherently assume that the insider threat is not rapidly evolving between model generation and use of the model in detection. Yet there is a large body of research that illustrates that the insider threat changes significantly after some types of precipitating events, such as layoffs, significant restructuring, and plant or facility closure. To capture this temporal evolution of user-system interactions, we use an unsupervised learning framework to evaluate whether potential insider threat events are triggered following precipitating events. The analysis leverages a bipartite graph of user and system interactions. The approach shows a clear correlation between precipitating events and the number of apparent anomalies. The results of our empirical analysis show a clear shift in behaviors after events which have previously been shown to increase insider activity, specifically precipitating events. We argue that this metadata about the level of insider threat behaviors validates the potential of the approach. We apply our method to a dataset that comprises interactions between engineers and software components in an enterprise version control system spanning more than 22 years. We use this unlabeled dataset and automatically detect statistically significant events. We show that there is statistically significant evidence that a subset of users diversify their committing behavior after precipitating events have been announced. Although these findings do not constitute detection of insider threat events per se, they do identify patterns of potentially malicious high-risk insider behavior. They reinforce the idea that insider operations can be motivated by the insiders' environment. Our proposed framework outperforms algorithms based on naive random approaches and algorithms using volume dependent statistics. This graph mining technique has potential for early detection of insider threat behavior in user-system interactions independent of the volume of interactions. The proposed method also enables organizations without a corpus of identified insider threats to train its own anomaly detection system.

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