Symantec Corp. researchers said that the "Storm Trojan," aka "Peacomm," is now spreading via AOL Instant Messenger (AIM), Google Talk and Yahoo Messenger.

An alert to some Symantec customers pegged the new infection vector as "insidious" because the message -- such as the cryptic "LOL ;)" -- and the included URL can be dynamically updated by the attacker. Even worse, according to Alfred Huger, senior director of Symantec's security response team, "it injects a message and URL only into already-open windows. It's not just some random message that pops up, but it appears only to people [you are] already talking to. That makes the approach very effective."

Moreover, the server from which the malware is downloaded to the victim's PC can be quickly changed by the attacker using the Trojan's peer-to-peer (P2P) control channel. "Everything can constantly change," said Huger.

The newest attack by Peacomm follows an earlier campaign in January, when the Trojan got its nickname from e-mail subject headings that touted news of massive storms throughout Europe.

But one researcher traced the Trojan further back than that. According to an analysis by Joe Stewart, a SecureWorks senior security researcher, Peacomm is actually a spinoff of last year's "Nuwar" worm. "It's pretty much the same code," said Stewart.