MSN Messenger worm entices the unwary

Draws victims to malicious Web site

A relatively benign but effective Internet worm attacked users of Microsoft's MSN Messenger service Wednesday by exploiting a bug in Internet Explorer that was reported last year, but was only recently patched by Microsoft.

Dubbed the 'Cool Worm' by an early discoverer, the worm arrives as an MSN instant message that reads, "Go To http://www.masenko-media.net/cool.html NoW !!!" Clicking on the link opens a Web page with malicious Javascript code that rifles through the victim's MSN Contacts list, then messages every contact with the same "Go To..." invitation. The code also sends e-mail to the address mmargae@wanadoo.nl.

"It ripped through the office," says Drew Smith, network administrator at an online gaming firm that was hit Wednesday afternoon. Smith, the first to report the worm to security mailing lists, says his twenty person office was completely saturated within thirty seconds. "We're in a support office, so everyone sits in front of a computer. Most of the time everyone is bored, so they're going to click on it. It's going to go straight through everyone."

The malicious Web site was no longer operating Wednesday night, but another version of the worm was still spreading in the wild. This second variety arrives marked "URGENT" and refers victims to a Web site hosted by a Belgium ISP, with a URL ending in "dark.angel/cool.htm". That site was still operating at press time.

The Cool Worm spreads through the Microsoft Internet Explorer Same Origin Policy Violation vulnerability, reported by a security researcher called "ThePull" on December 19th, which went unacknowledged and unrepaired by Microsoft for months.

Microsoft's reluctance to acknowledge the bug was criticized by many in the security community. Last week, in what they described as an effort to spur Redmond to action, security gurus Tom Gilder and Thor Larholm released a demonstration of how a properly crafted Web page could exploit the unpatched bug to take over a user's MSN Messenger program. The example code was not a worm, but may have inspired the Cool Worm's author.

"This example has been made public to put pressure on MS to patch their vulnerabilities, that they are fully aware of," Gilder wrote.

Microsoft released a patch for the vulnerability on Monday. Installing the patch reportedly blocks the Cool Worm.

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