Email worm joins Blaster attack on Windows

Shot by both sides

A new variant of the Sobig worm is spreading rapidly across the Internet this afternoon.

Sobig-F, like its predecessors, can spread via either email or (less commonly) network shares.

Infectious emails come with a variety of subject lines (eg. 'Your details', 'Re: Approved', 'Re: Your application', 'Re: Wicked screensaver', 'Re: That movie', 'Thank you!', etc.) and an infectious .pif or .scr attachment. Launching the infected attachment infects a computer, natch

Sobig-F scans infected PCs for email addresses prior to blasting out copies of itself using its own SMTP client using spoofed email addresses filleted from the compromised PC.

Advisories by F-Secure and Sophos provide more information.

The worm is spreading rapidly. Managed services firm MessageLabs had blocked Sobig-F 36,227 times since spotting it yesterday.

We're getting sick of saying this, but Sobig-F is a Windows-only menace. Mac, Linux, OS/2 and Unix users are immune.

For Windows users it's the now familiar routine of updating viral software, blocking executables at the gateway and crossing their fingers that the current viral plague will subside.

A substantial number of firms are beginning to question whether this approach is appropriate given the current onslaught of malicious code.

Firms like MessageLabs and Avecho.com argue that the only sensible place to block malicious code is before it reaches users whilst a new generation of behaviour blocking firms are coming forward with technology to lock down Windows PCs. ®

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