If you pay attention to the news, then you know that network security is an important issue. It seems that every day brings a new account of compromised networks and compromised personal information; new viruses, worms, trojans, phishing attacks, and the like. We hear reports on identity theft, criminal use of botnets (networks of hijacked computers), and foreign countries’ concerted efforts to break into defense networks. Clearly, attackers, motives, and methods vary, but the dangers are real.