Yimp

Yimp is an Internet worm, which spreads through instant messages sent using the AIM or Yahoo! Messenger application. The victim receives a message containing a link to a malicious executable. Once he or she clicks on a link and runs a file, the worm immediately installs itself to the computer. It initiates a spreading routine sending bogus messages to all the user's contacts and runs a payload. Yimp downloads from the Internet and executes potenitally harmful files, disables several computer services and blocks access to popular antivirus and security-related web sites. The worm automatically runs on every Windows startup.