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By Joris Evers, 7 December 2005 09:00

NEWS

A new worm that targets users of AOL Instant Messenger is believed to be the first that actually chats with the intended victim to dupe the target into activating a malicious payload, IM security vendor IMlogic warned on Tuesday.

According to IMlogic, the worm, dubbed IM.Myspace04.AIM, has arrived in instant messages that state: "lol thats cool" and included a URL to a malicious file "clarissa17.pif". When unsuspecting users have responded, perhaps asking if the attachment contained a virus, the worm has replied: "lol no its not its a virus", IMlogic said.

The malicious file disables security software, installs a backdoor and tweaks system files, the company said. Then it starts sending itself to contacts on the victim's buddy list.

But the worm is programmed so that the infected user cannot see the messages that are being sent out by the worm, according to IMlogic.

Andrew Burton, director of product management at IMlogic, said: "This is a first." This worm is not widespread but attackers are just trying out this new technique, he said. "We will see one or two instances of an attack, there will be a refinement and then there will be an outbreak."

The inclusion of an IM bot is another sign that IM worms are becoming more sophisticated. Another worm, also spotted on Tuesday, takes a more traditional route: it spreads under the guise of a holiday greeting card, IM security specialist Akonix Systems said on Tuesday.

The holiday worm, dubbed Aimdes.E, targets AIM users and arrives with the message: "The user has sent you a Greeting Card, to open it visit:" followed by a link. Once the target clicks on the link, the worm installs itself on the system. It opens a backdoor on the computer and sends itself to contacts on the buddy list, Akonix said.

Advice to users is to be careful when clicking on links in IM messages - even when they seem to come from friends - and to use up-to-date antivirus software. When receiving a link in an instant message, the best practice is to verify with the sender if the link was sent intentionally or not.

Joris Evers writes for CNET News.com