The network worm named, I-Worm.Swen is causing an epidemic. The malicious program spreads using email, the Kazaa file-sharing network and via IRC channels.
Infected messages appear to have been sent from various Microsoft services, including for example MS Technical Assistance, Microsoft Internet Security Section, etc. Message text advises users to install a "special patch" from Microsoft. The "patch" is included as an attachment.
Kaspersky Labs experts currently attribute over 30,000 computer infections worldwide to I-Worm.Swen. The number of infections continues to rise.
More information:
Network Associates Virus Information