Bagle Worm Resurfaces -- More Variants Expected

The Bagle family of worms, fairly dormant for the past few months, has spawned a flurry of variants that are kicking up a storm in the wild. And with the release of the worm's source code, more are expected to be on the way.


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The Bagle family of worms, fairly dormant for the past few months, has spawned a flurry of variants that are kicking up a storm in the wild.

Several new versions of the Bagle worm have been released onto the Internet in the past few weeks, bringing new life to the Bagle family of worms, which had been quiet since late in February. They also are spreading successfully and receiving medium to severe threat ratings from anti-virus vendors.

''It just goes to prove that old tricks still work,'' says Ken Dunham, director of malicious code at iDefense, Inc., a security intelligence company based in Reston, Va. ''The variants are having good success in the wild and that's disturbing. After all this time, everybody knows about attachments and they know about security, but this worm is still spreading. That's disturbing.''

Steve Sundermeier, a vice president at Central Command, an anti-virus company based in Medina, Ohio, says they have logged in Bagle-AE, Bagle-AF, Bagle-AG, Bagle-AH and Bagle-AI. The worm's author or authors dropped the worm's source code into two of the recently released variants, feeding other virus writers who may want to write and release their own Bagle variant.

Some security analysts speculate that the Bagle author, trying to avoid prosecution, was copying the creator of the MyDoom worm family when he released the source code. By distributing the source code to thousands or even hundreds of thousands of machines, the author could more easily try to deny responsibility for any worm code found on his machine.

But regardless of his strategy, the release of the source code could mean a run of Bagle variants is on its way.

''We expect to see many new Bagle variants in the months to come,'' says Dunham. ''Once the source code has been made available, it's easy to make new variants and distribute them.''

And the new variants, though not as wide spread and disruptive as their earlier siblings, are still causing problems.

Bagle-AI, which was first seen in the wild just a few days ago, garnered a medium-threat ranking and spread rapidly. Sundermeier says, though, that the variant slowed down on Tuesday and the ranking has been dropped to a low-to-medium threat.

The Bagle variants are mass-mailing worms that also can spread over file sharing applications. They arrive with .exe, .ser and .zip files attached. Once they have a foothold in a computer, the worms search out anti-virus and personal firewall applications and shut them down. Some of the variants also try to connect to a German Web site to download modifications to itself. A backdoor is opened in the compromised computer so spam or other viruses can be sent without the owner's knowledge or consent.

When Bagle first hit the scene this winter, it caused a lot of problems. Variant after variant hit the wild when the worm author got into a spitting contest with the Netsky author. The worm war that ensued between the two created a disruptive series of attacks on the Net.

The alleged author of the Netsky worms was arrested in Germany this spring, and most security analysts thought that would bring an end to the string of variants from both Netsky and Bagle.

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