New Worm Masquerades As Security UpdateNew Worm Masquerades As Security Update

A new worm that tries to take advantage of Windows users anxious to get their hands on security updates began making the rounds on Thursday, several antivirus firms confirmed.

The worm, which goes by a variety of names, including Swen, W32/Swen@MM, Gibe, and W32/Gibe-F, can pose as an E-mail from Microsoft bearing a bogus security update as a file attachment.

It spreads in several ways, including the traditional mass-mailing method of stealing addresses from Outlook address books on compromised machines, but also propagates over Internet Relay Chat and peer-to-peer networks such as Kazaa. Successful infections attempt to steal account information, including usernames and passwords.

The worm also exploits a 2-year-old vulnerability in Windows--for which a fix is available from Microsoft--that allows it to auto-execute on unpatched PCs. In those situations, the receiving system is infected even if its user doesn't open the attached file.

Most anti-virus vendors have tagged Swen as a relatively low risk. Symantec rates it as only a 2 on its 1-through-5 scale, while both Trend Micro and Network Associates list it as "low," although Network Associates ranks it as a "medium" threat to home users.

"Swen preys upon the good nature of individuals who want to patch their computer in the wake of new vulnerability and virus announcements," said Ken Dunham, the malicious code intelligence manager at security firm iDefense.

Antivirus software suppliers have already posted updates to their products' definition files to detect Swen.