  Modeling and analyzing security of networked systems is an important problem
in the emerging Science of Security and has been under active investigation. In
this paper, we propose a new approach towards tackling the problem. Our
approach is inspired by the {\em shock model} and {\em random environment}
techniques in the Theory of Reliability, while accommodating security
ingredients. To the best of our knowledge, our model is the first that can
accommodate a certain degree of {\em adaptiveness of attacks}, which
substantially weakens the often-made independence and exponential attack
inter-arrival time assumptions. The approach leads to a stochastic process
model with two security metrics, and we attain some analytic results in terms
of the security metrics.
