The electrical network is a critical infrastructure which is highly interconnected and strongly interdependent on other basic infrastructures on which basic human activities depend. As a result, this network is often targeted by terrorist attacks. The occurrence of events (that may affect the system) due to terrorism must be considered in power system security assessment. In this way, proper decisions in the planning and operation of the power system can be taken so that an appropriate balance between operative cost and robustness in the case that a terrorist act affects the system can be reached. In this paper we present a methodology that enables us to assess the power system security with regard to the possibility of terrorist acts, considering also the uncertainties associated with load and generation. The method is a validated Western System Coordinating Council (WSCC) nine-bus test system, taking as an example the terrorism conditions of the Colombian electricity infrastructure.