In the war against terrorist enemies, the United States currently is using a traditional defensive approach: engaging in formal military ground battles with adversaries such as al-Qaeda. By conducting a formal military operation, powerful military forces ideally should defeat terrorists, break up terrorist cells, remove their home bases, disperse leaders, and severely degrade the terrorist groups’ ability to wage attacks against the United States. A traditional military war normally involves two parties with known geographical locations and concentrated battle areas. A victory occurs when an enemy is defeated. However, the war on terrorism represents an opposite situation: without geographic concentration. Modern terrorists operate across national borders and have access to funding and advanced technology with global reach. Terrorists such as al-Qaeda lack geographic homes, which mean the battlefield is geographically dispersed. Furthermore, in addition to using conventional weapons, they increasingly use modern information technology, particularly the Internet, to wage their battles. They ride the back of the Web and use advanced communications to distribute their thoughts or views, gather support, recruit new members, and move immense financial funds from one place to another. According to Weimann (2006), many terrorist groups have their own Web sites on the Internet, which they use to teach their members to prepare computer viruses, worms, Trojan horses, sniffers, and other malicious programs that multiply and cause potentially severe damages. They thus consider the capabilities of the Web as offensive mass weapons that can undermine worldwide actions. The modern Internet penetrates all levels of society, such that information flows continuously and seamlessly across political, ethnic, and religious divides. Because of the global nature of cyberspace, it provides a new platform on which terrorists can wage battles. In this chapter, we examine the role of the Internet as a battlefield and analyze the course of war in cyberspace. We model the Internet structure and determine that the Internet needs a self-immunization mechanism that can self-detect illegal or criminal activities online.