SECUSIM: A tool for the cyber-attack simulation. The cyber attack simulation tool, SECUSIM, is presented for specifying attack mechanisms, verifying defense mechanisms, and evaluating their consequences. The tool has been successfully developed by employing the advanced modeling and simulation concepts such as SES/MB (System Entity Structure / Model Base) framework, DEVS (Discrete Event System Specification) formalism, and experimental frame. SECUSIM is currently implemented on the basis of Visual C++ and enables a simulation of twenty attack scenarios against hundreds network components