Original URL: http://www.theregister.co.uk/2004/09/22/opt-out_exploit/

Click here to become infected

Opt-out button in spam used to run exploit

By John Leyden

Posted in Security, 22nd September 2004 09:15 GMT

Users should be wary of pressing the 'click here to remove' link on spam messages because it serves to confirm to spammers that junk mail messages are being read. Such email addresses can be sold at a premium to other spammers.

That's reason enough to simply delete spam messages, but a junk mail message doing the rounds today provides an even more compelling reason. Selecting the 'click here to remove' link on messages blocked by MessageLabs today triggers an attempt to load malicious code onto potentially vulnerable Windows PC.

MessageLabs is blocking spam linking to the domains www. xcelent.biz (space deliberately inserted) which, if users click on the remove link and scroll down the page triggers a DragDrop JavaScript exploit. This uses an IE bug to download and run an EXE file, currently been analysed by MessageLabs.

Alex Shipp of MessageLabs writes: "I have not finished analysing the EXE currently hosted (currently called windows-update.exe), but the spammers can change this at any time by uploading a new Trojan. Typically, your machine may be turned into an open proxy, have passwords extracted, and keyloggers installed.

"So not only do you confirm your email address to the spammers, you also get to host their next spam run, and get your bank account cleaned out," he adds.

The US's CAN-SPAM Act requires junk mailers to put an opt-out link on their wares. It comes as little surprise that this feature is been taken advantage of in a social engineering exploit; but it does illustrate the security problems of the opt-out approach that were always apparent to security experts - and ignored by legislators. ®

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