Information systems now form the backbone of nearly every government and private system — from targeting weapons to conducting financial transactions. Increasingly these systems are networked together allowing for distributed operations, sharing of databases, and redundant capability. Ensuring these networks are secure, robust, and reliable is critical for the strategic and economic well being of the Nation. The blackout of August 14, 2003 affected 8 states and fifty million people and could cost up to $5 billion [2]. The DOE/NERC interim reports [3] indicate the outage progressed as a chain of relatively minor events consistent with previous cascading outages caused by a domino reaction [4]. The increasing use of embedded distributed systems to manage and control our technologically complex society makes knowing the vulnerability of such systems essential to improving their intrinsic reliability/survivability. Our discussion employs the power transmission grid.