Less than two days after it first appeared on the Internet, the W32.Blaster worm already spawned a new variation that is also spreading, according to warnings from antivirus vendors.
The new variation of Blaster was identified Wednesday, 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 is known yet about how the new Blaster version differs from the original, according to Chris Belthoff, senior security analyst at Sophos.
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 colorful 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, according to a company spokesman.
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 have 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 posted update virus identity files to detect both new threats Wednesday.
The emergence of new versions of the Blaster worm complicates the job of blocking attacks for customers who haven't patched their vulnerable Windows systems, Belthoff said.
"We're starting to see the floodgates open. We were hopeful that Blaster would be the first and last, but it seems like that's not going to happen," he said.
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 http://www.microsoft.com/technet/security/bulletin/MS03-026.asp.)
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, according to Symantec's Huger.