The technological age has forced the U.S. to engage a new set of national security challenges. Several potential adversaries have cyberspace capabilities comparable to those of the U.S., and are constantly conducting surveillance, gathering technical information, and mapping critical nodes that could be exploited in future conflicts. How can the U.S. government best defend against future cyber attacks? Recent policy documents set out a strategy for securing all of cyberspace, which experts argue is impossible to implement, but also unnecessary. This thesis seeks to move the discussion beyond this stalemate by undertaking an analysis of the vulnerability of cyberspace to terrorist attacks. The first analysis examines the Code Red Worm and the Slammer Worm. These two worms were selected because they were highly destructive and spread faster than normal worms, making them well suited for assessing the existing security of computers and networks. The next analysis examines a staged cyber attack on critical infrastructure, entitled Attack Aurora. In the staged Aurora attack, researchers from the Department of Energy’s Idaho lab hacked into a replica of a power plant’s control system. This attack is the most recent staged attack and facilitates an analysis of vulnerabilities of critical infrastructures to cyberterrorism.