Compromised U.S. computers: 480,000

Main crime use: Also known as IRCBrute, or an autorun worm, this backdoor worm makes copies of itself on the system and any removable drive it finds -- and anytime the removable drives are accessed, it executes automatically. An effective spreading mechanism, Hamweq creates registry entries to enable its automatic execution at every startup and injects itself into Explorer.exe. The botmaster using it can execute commands on and receive information from the compromised system.