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Security experts have spotted the first attempts to create an Internet worm that propagates using instant messages and exploits a recently disclosed flaw in Microsoft software.

Researchers at The SANS Institute's Internet Storm Center (ISC) have had two reports of users receiving messages on America Online's AOL Instant Messenger service that lured them to Web sites containing malicious code, says Johannes Ullrich, chief technology officer at SANS ISC.

The messages told the users to "Check out my profile, click GET INFO!"

When visiting the Web sites, the malicious code would attempt to install "backdoor" software on the user's PC that gives remote attackers total control over the machine. Additionally, messages containing a link to the site would be sent out to all contacts on the victim's instant messenger contacts list, Ullrich says.

The malicious code is embedded in a JPEG image and exploits a security flaw in the way many Microsoft applications process such images. Microsoft identified and patched the flaw on September 14, but users have complained that patching is onerous because several applications, including Office and Windows, require separate patches.

Hackers Hard at Work

These first attempts to exploit the JPEG flaw using instant messaging appear to have failed. There have been no further reports of users getting the messages and the two AOL Instant Messenger user profile Web pages that contained the harmful images are no longer available, Ullrich says.

"People should be worried about the next attempt," Ullrich says. These first attempts show that people are actively working on this type of attack, he says.

FaceTime Communications, a provider of instant messaging security applications, also has not seen the attacks hit any of its customers, says Christopher Dean, senior vice president of marketing and business development at the Foster City, California-based company.

"We have not received reports from our customers, but we are alerting them about the threat at the moment," he says. "We think it is a pretty significant threat. You can basically completely take over the machine."

The warning about attempts to exploit the latest Microsoft vulnerability via instant messaging follows warnings earlier this week about hackers seeding pornography Usenet news groups with malicious JPEG images. Users who unwittingly downloaded the images could also have backdoor software installed on their computers.