Dependencies and interdependencies between critical infrastructures are difficult to identify and model because their effects appear infrequently with unpredictable consequences. The addition of cyber attacks in this context makes the analysis even more complex. Integrating the consequences of cyber attacks and interdependencies requires detailed knowledge about both concepts at a common level of abstraction.CISIApro is a critical infrastructure simulator that was created to evaluate the consequences of faults and failures in interdependent infrastructures. This chapter demonstrates the use of CISIApro to evaluate the effects of cyber attacks on physical equipment and infrastructure services. A complex environment involving three interconnected infrastructures is considered: a medium voltage power grid managed by a control center over a SCADA network that is interconnected with a general-purpose telecommunications network. The functionality of the simulator is showcased by subjecting the interconnected infrastructures to an ARP spoofing attack and worm infection. The simulation demonstrates the utility of CISIApro in supporting decision making by electric grid operators, in particular, helping choose between alternative fault isolation and system restoration procedures.