AIM worm exhibits new, nasty tactics

A worm found spreading via America Online's Instant Messenger is carrying a nastier punch than usual, a security company has warned.

The unnamed worm delivers a cocktail of unwanted software, including a so-called rootkit, security experts at FaceTime Communications said on Friday. A rootkit is a tool designed to go undetected by the security software used to lock down control of a computer after an initial hack.

"A very nasty bundle is downloaded to your machine" when you click on the worm link, said Tyler Wells, senior director of engineering at FaceTime. "This is the first time that we have seen a rootkit as part of the bundle of applications that is sent to your machine. It is a disturbing trend."

IM worm and malicious code attacks are happening more than ever before. The number of threats detected for instant-messaging and peer-to-peer networks rose 3,295 per cent in the third quarter of 2005, compared with last year, according to a recent report from security provider IMlogic.

In addition to the 'lockx.exe' rootkit file, the new worm delivers a version of the Sdbot Trojan horse, said FaceTime, which sells products to protect instant-messaging traffic. Sdbot opens a backdoor on the infected PC. The worm also places several spyware and adware applications, including 180Solutions, Zango, the Freepod Toolbar, MaxSearch, Media Gateway and SearchMiracle, the company added.

All that unwanted software can eat up system resources, slowing down the PC, Wells said. Also, the malicious applications will attempt to disable security programs and change the search page on the user's web browser, FaceTime said.

The worm was spotted in an AOL IM chatroom and infected one of the PCs that FaceTime uses for worm bait. The company said it also has seen the pest hit other computers. "It is still out there, and it is definitely something the user should be leery of," Wells said. "The rootkit is designed to not be detected, and that is the scary part."

Worms on IM networks can spread rapidly. They appear as a message from a buddy with a link that looks innocent but in fact points to malicious code somewhere on the internet. Once the user clicks on the link, malicious code is installed and runs on the computer. The worm then spreads itself by sending messages to all names on the victim's contact list.

The 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