The recent white paper by the Honeynet Project called "KYE: Tracking Botnets" introduced a method to track botnets. A botnet is a network of compromised computers that can be remotely controlled by an attacker. Due to their immense size (tens of thousands of systems can be linked together), botnets can pose a severe threat to the community when used for Denial-of-Service (DoS) attacks. Initial research in this area demonstrated that botnets are sometimes used to send out spam emails and can also be used for phishing attacks. During a study in October 2004, email security company CipherTrust suggested that 70% of monitored phishing spam was sent through one of five active botnets, but our own observations suggest that many more botnets are in use for spam operations. Although not the analysis of one single incident, in this section we present our observations on the tools and techniques used by attackers engaged in phishing via botnets.