Bagle Worm Resurfaces -- More Variants Expected

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

Several new versions of the Bagle worm have been released onto theInternet in the past few weeks, bringing new life to the Bagle family ofworms, which had been quiet since late in February. They also arespreading successfully and receiving medium to severe threat ratingsfrom 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 intelligencecompany based in Reston, Va. ''The variants are having good success inthe wild and that's disturbing. After all this time, everybody knowsabout attachments and they know about security, but this worm is stillspreading. That's disturbing.''

Steve Sundermeier, a vice president at Central Command, an anti-viruscompany 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 authorsdropped the worm's source code into two of the recently releasedvariants, feeding other virus writers who may want to write and releasetheir own Bagle variant.

Some security analysts speculate that the Bagle author, trying to avoidprosecution, was copying the creator of the MyDoom worm family when hereleased the source code. By distributing the source code to thousandsor even hundreds of thousands of machines, the author could more easilytry to deny responsibility for any worm code found on his machine.

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

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

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

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

The Bagle variants are mass-mailing worms that also can spread over filesharing applications. They arrive with .exe, .ser and .zip filesattached. Once they have a foothold in a computer, the worms search outanti-virus and personal firewall applications and shut them down. Someof the variants also try to connect to a German Web site to downloadmodifications to itself. A backdoor is opened in the compromisedcomputer so spam or other viruses can be sent without the owner'sknowledge 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 aspitting contest with the Netsky author. The worm war that ensuedbetween the two created a disruptive series of attacks on the Net.

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

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