Abstract-We analyze sets of intrusion detection records observed on the networks of several large, nonresidential organizations protected by a form of intrusion detection and prevention service. Our analyses reveal that the process of intrusion detection in these networks exhibits a significant degree of burstiness as well as strong memory, with burstiness and memory properties that are comparable to those of natural processes driven by threshold effects, but different from bursty human activities. We explore time-series models of these observable network security incidents based on partially observed data using a hidden Markov model with restricted hidden states, which we fit using Markov Chain Monte Carlo techniques. We examine the output of the fitted model with respect to its statistical properties and demonstrate that the model adequately accounts for intrinsic "bursting" within observed network incidents as a result of alternation between two or more stochastic processes. While our analysis does not lead directly to new detection capabilities, the practical implications of gaining better understanding of the observed burstiness are significant, and include opportunities for quantifying a network's risks and defensive efforts.Index Terms-bursty processes, cyber risk assessment, cyber security, estimating undetected malware, malware detection model, predictive models for cyber intrusions
I. INTRODUCTION AND MOTIVATION
A. MotivationWe explore approaches to modeling the detection process of cyber infections, i.e., presence of malicious softwaremalware -on a computer network. Often, this process is performed by a specialized organization -Managed Security Service Provider (MSSP) [1] -that monitors computer networks, analyzes the information obtained from the network, detects intrusions and activities of malware on the network, and reports such detections to the operators of the network who then take measures necessary to recover from the intrusion. As this research is based on empirical data provided to authors by a MSSP covering several large, non-residential networks, hereafter we use the term MSSP when referring to a network's cyber defenders.