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Interdependent Security Risk Analysis of Hosts and Flows Detection of high risk hosts and flows continues to be a significant problem in security monitoring of high throughput networks. A comprehensive risk assessment method should take into account the risk propagation among risky hosts and flows. In this paper this is achieved by introducing two novel concepts. The first is an interdependency relationship among the risk scores of a network flow and its source and destination hosts. In one hand, the risk score of a host depends on risky flows such a host initiates and is targeted by. On the other hand, the risk score of a flow depends on the risk scores of its source and destination hosts. The second concept, which we call flow provenance, represents risk propagation among network flows which takes into account the likelihood that a particular flow is caused by other flows. Based on these two concepts, we develop an iterative algorithm for computing the risk score of hosts and network flows. We give a rigorous proof that our algorithm rapidly converges to unique risk estimates, and provide its extensive empirical evaluation using two real-world datasets. Our evaluation shows that our method is effective in detecting high risk hosts and flows and is sufficiently efficient to be deployed in high throughput networks.