Giovanna Dondossola*, Judit Szanto**, Marcelo Masera***, Igor Nai Fovino*** Rivista: Special Issue of the THE INTERNATIONAL JOURNAL OF CRITICAL INFRASTRUCTURES (IJCI), Inderscience Publishers, Vol 4, N. 1/2 2008 * CESI RICERCA ** CONSULENTE *** JOINT RESEARCH CENTRE – EUROPEAN COMMISSION (JRC) Power station control and management systems represent key elements for guaranteeing the security of the power grid infrastructure. Intrinsically conceived to support the continuous provision of power in secure conditions, those systems today make intensive use of information and communication systems and are therefore exposed to related accidental and intentional cyber threats. This paper describes a simulation of cyber attacks conducted in the CESI RICERCA laboratory testbed on a prototypical substation control infrastructure with the purpose of testing their feasibility and illustrating their impact on the control system services. A set of attack scenarios targeting several subsystems has been experimented, with different simulated threat motivations and different degrees of impact on the global substation service. The paper reports some considerations about the consequences of the implemented attacks, focusing on different facets of the problem, in an effort to elucidate the full significance of the potential cyber threats. Keywords: power substation control system security; cyber attacks; resilient control architectures; risk evaluation.