A worm that zipped through America Online's instant message network Tuesday was quickly shut down by the Internet service provider, a security company said Wednesday.

Gabby.a, a worm very much like the Kelvir family that's been knocking at Microsoft's instant messaging network (and actually knocked the Microsoft-based Reuters messaging service offline for a day two weeks ago), had been spreading through AOL's IM users.

With the help of IMLogic's Threat Center, the malicious code was detected; AOL then blocked further propagation at its servers.

Users received a message with text that read "Hey check out this!" with a link that downloaded and installed the payload, a variant of the infamous Spybot worm which can open a backdoor to the infect machine, use the compromised PC as a proxy, and eliminate Windows processes and services, such as those for anti-virus and firewall software, making the machine even more vulnerable to follow-on attacks.

America Online is one of the participating vendors in the IMLogic Threat Center, a centralized database of IM and peer-to-peer threats and exploits. Other companies participating in the Threat Center include Microsoft, Symantec, Yahoo!, and IBM.