New Blaster worm variant on the loose

Less than two days after it first appeared on the Internet, the W32.Blaster worm has already spawned a new variation that is also spreading, according to warnings from antivirus vendors.

The new variation of Blaster was identified yesterday, according to antivirus company, Sophos.

Like the original worm, the variation affects computers running Microsoft's Windows XP and Windows 2000 operating systems.

Blaster takes advantage of a known vulnerability in a Windows component called the DCOM (Distributed Component Object Model) interface, which handles messages sent using the RPC (Remote Procedure Call) protocol.

Windows XP users infected with Blaster report frequent system reboots and messages about "System Shutdown". Both Windows XP and Windows 2000 users may experience significant system slow downs when using Windows or surfing the Internet if their machine is infected, according to Alfred Huger, director of engineering at Symantec Security Response.

Little was known yet about how the new Blaster version differed from the original, senior security analyst at Sophos, Chris Belthoff, said. Dubbed W32/Blaster-B, the new worm works like the original Blaster, but comes packaged as a file called teekids.exe as opposed to msblast.exe used by the original worm.

Blaster-B also replaces an internal message stating "LOVE YOU SAN" with some colourful suggestions for Microsoft Chairman and Chief Software Architect. Bill Gates, according to Sophos.

Antivirus company, Symantec, also identified the Blaster-B variant and rated it a Category 2 "low" threat, a company spokesman said. A second new threat is named W32/RpcSpybot-A. It exploits the same vulnerability as Blaster so it's not considered a variation.

It contains code that creates a backdoor on infected machines that could give an attacker control over that machine, Sophos said.

RpcSpybot-A uses the same exploit as the worm, but is an IRC (Internet Relay Chat) trojan that scans the Internet for vulnerable systems, exploits the RPC DCOM security hole, then uses IRC to remotely control the infected systems for use in a denial of service attack, according to Symantec's Huger.

Sophos researchers were still analyzing RpcSpybot-A and did not yet know what other actions it might perform on infected systems, Belthoff said.

Similar threats that use the DCOM security hole had been circulating on the Internet for weeks, predating the release of Blaster, Huger said. Neither Sophos nor Symantec knew of any infections stemming from RpcSpybot-A.

Sophos has posted update virus identity files to detect both new threats.

The emergence of new versions of the Blaster worm complicated the job of blocking attacks for customers who hadn't patched their vulnerable Windows systems, Belthoff said.

"We're starting to see the floodgates open," he said. "We were hopeful that Blaster would be the first and last, but it seems like that's not going to happen."

Belthoff and others recommend that those using vulnerable versions of Windows XP and Windows 2000 apply a software patch released by Microsoft in July. (See

Users can also search their hard drive for the worm file, msblast.exe or the new teekids.exe. Users who find the file should delete it and immediately obtain and install the appropriate patch from Microsoft, Huger said.

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Paul Roberts

IDG News Service
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