Network security comprises the growing science of protecting data stored and transmitted across information networks. Security of data (and voice) transmissions has become an increasingly important issue as the Internet has expanded, and once-private corporate networks conduct a great deal of business in public cyberspace over the Internet and wide area networks. The danger of information being intercepted, corrupted, or misappropriated has escalated, as has the fear of hackers breaking into servers and altering source code published on Web sites or conducting Denial-of-Service attacks. As a result computer and network security procedures, practices, and technologies have developed into a science of their own. Today computer and network security take many forms and offer varying levels of protection, ranging from physical measures such as data-drive locks to access codes, user identification passwords, authentication devices, firewalls, data encryption, router access-control lists (ACLs), virtual LANS (VLANS), and Virtual Private...