Commtouch: Bagle worm still thriving after three years

Computerworld - More than three years after its debut, the Bagle worm still plagues users because its creator cranks out hundreds of variants each day that can overwhelm antivirus defenses, security company Commtouch Software Ltd. said today.

But a rival security firm contested that claim, saying that many of the variants never get through computer defenses.

Bagle, a worm that first appeared in January 2004, remains a threat, said Sunnyvale, Calif.-based Commtouch in a report published today (download PDF). Despite its age, Bagle continues to infect PCs because attackers are writing and releasing large numbers of variants daily -- more than 1,000 have been released on a single day at least twice since Jan. 9. On average, 625 variants are released per day, each of which is attached to a very small number of spammed e-mailed messages.

"Common anti-virus techniques depend on prior knowledge of malware to devise tools to block future outbreaks," Commtouch said in the report. "Since server-side polymorphs like Bagle distribute each variant in a small number of e-mails and then switch to new variants, by the time traditional AV vendors can develop a signature or heuristic appropriate for one variant, its lifecycle has ended and new variants are being propagated."

Commtouch identified approximately 30,000 distinct Bagle variants in the nearly seven weeks between Jan. 9 and Feb. 25. "The recent burst of 30,000 variants shows that Bagle has adopted the server-side polymorphic form and is sending intense waves of variants, Haggai Carmon, Commtouch's vice president, said in a statement.

The high volume of variants gives attackers the advantage, added Commtouch, not only because of their sheer number, but also because the low-volume distribution of any one Bagle variant lets the malware fly under the radar. The firm said it has seen instances where a variant was attached to only a few hundred messages.

To create a signature, antivirus vendors require a sample of the malicious code; those samples must be obtained from users, other security researchers or a vendor's own honeypot systems -- PCs deliberately left unguarded in the hope that they will snare malware. "Numerous variants never even reach the stage of being analyzed by the AV vendors to create a signature or heuristic," Commtouch said.

That point is moot, according to a security researcher at Symantec Corp. "Someone sitting at the gateway, like Commtouch, would see a lot of this [Bagle activity]," said Dave Cole, director of Symantec's security response. "But Bagle's payload is an executable, and even smaller businesses don't let executables through the gateway. These threats never get through, so they don't really matter because they're categorically blocked."