Update Stop us if you've heard this before, but there's another prolific email worm loose on the Internet today.

Sobig-E differs from its predecessors, the Sobig-B (aka 'support@microsoft.com') and Sobig-C (aka 'bill@microsoft.com') worms, by spreading itself in the form of a ZIP file. This time around infectious emails sent out by Sobig-E pretend to come from support@yahoo.com or another spoofed email address.

The worm is spreading rapidly, with many vendors upgrading the severity ratings they attach to the worm this morning. At the time of writing, managed services firm MessageLabs has blocked 22,156 copies of the worm over the last 24 hours.

Sobig-E normally spreads via emails with randomised subject lines (such as Re: Documents and Re: Re: Movie) and . zip attachments containing infectious .scr and .pif files. Like its predecessors, Sobig-E has a built-in expiry date - in this case 14 July. Click on the infectious attachments and you catch the pox.

As usual, the worm affects only Windows PCs. Linux and Mac users are immune.

On infected PCs Sobig-E sends email to addresses collected from files with the following extensions: .wab, .dbx, .htm, .html, .eml, .txt. This trick is the likely reason behind the worm's rapid rise to prominence.

Sobig-E appears to also have the ability to spread via
network shares and uses its own SMTP mail engine for sending email to further propagate.

So what to do?

Don't run suspicious email attachments and update your AV signature files.

It's as simple as that really.

A write-ups of the varmint by Symantec provides more detailed information. ®

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