Microsoft’s MSN Messenger and America Online’s Instant Messenger services are being targeted by malicious messages containing links that could infect a computer with a Trojan horse or dangerous worm.

The latest threat is a Trojan called Kirvo, which arrives in the form of an instant message from someone on the user’s “friends” list. The message contains a link to a Web site, which, if clicked on, loads a copy of Kirvo onto the computer, according to an advisory from security company Symantec. Kirvo is preprogrammed to then fetch a copy of Spybot, a dangerous worm that can take advantage of software vulnerabilities to spy on the user. Full Story