Security vendors have reported several new variants of the worm infecting PCs running Microsoft's Windows 2000 operating system. Groups of virus writers are competing to cause the most damage, according to one security company, although the worm appears less severe than some first feared.
F-Secure said on Wednesday that it had identified three "families" of worms -- Zotob, Bozori and Ircbot -- all stemming from a vulnerability reported Aug. 9 in Microsoft's Windows 2000 Plug and Play software. The worm will cause infected systems to continually reboot, antivirus vendors said.
The Finnish security company has seen 11 variants of the worms altogether, including four that appeared Wednesday morning in Europe, said Mikko Hypponen, F-Secure's chief research officer.
The extent of the damage is hard to measure, he said, but the worm does not appear to be as serious as the Sasser or Blaster worms of recent years, in part because it does not affect the more widely used Windows XP operating system.
Still, it is the worst virus outbreak so far this year, Hypponen said. A "botwar" appears to have broken out in which three virus-writing "gangs" are competing to create a worm variant that causes the most damage, he said. The latest variants of the Bozori worm are even removing "competing" viruses from users' machines, according to F-Secure.
The worms affect only Windows 2000 computers, Microsoft and antivirus vendors said. Microsoft released a patch for the Plug and Play vulnerability (MS05-039) on Aug. 9, but home users are notoriously slow to patch their machines, and some businesses have been reluctant to do so for fear of "breaking" custom applications, security experts said.
On Tuesday, Microsoft contested reports that any new viruses have emerged, saying all the worms are variants of Zotob. It continued to rate the issue as "a low threat for customers," and said it had seen only low rates of infection. Still, it ranked the original flaw in its software as "critical."
However, McAfee's antivirus response team raised its risk assessment to "high" for one variant of the IRCBot worm. Late Tuesday it said it had received more than 150 reports of the worm either being stopped or intercepting users' PCs, mostly in the U.S. but also from Europe and Asia.
Trend Micro Inc. received reports of infections from three corporate customers, which it considers a low level, a spokesman for the company in Tokyo said Wednesday. None of the reports were from major corporations, he said.
Media outlets have been among the hardest hit by the worm, including Time Warner's CNN news network, The New York Times and the ABC television network, a unit of The Walt Disney Co., according to a report in Wednesday's Wall Street Journal newspaper.
This may be because one of the variants, Zotob.C, can masquerade as a picture file, suggested Alan Paller, director of Research at The SANS Institute.
"If an early infectee had an email list with reporters at all the major news services, that would start the cascade. News organizations do not have radical email attachment limits (like a rule banning all picture attachments) because they get legitimate pictures," Paller wrote in an e-mail.
The IRCBot worm first appeared seven days after the Microsoft vulnerability was first reported, marking the fastest time to create a mass propagating exploit, McAfee said. The first successful mass exploit for the Sasser worm took two weeks to appear, the company said.
Infections continued to be reported at large organizations, especially in the U.S., F-Secure said. These most likely stemmed from laptops carried inside the organizations' perimeter firewall, it said.
The worms replicate by scanning machines at port 445/TCP and, when a victim is found, use the exploit code to download the main virus file via FTP (file transfer protocol). The virus then sets up an FTP server on the infected machine and starts scanning for more targets to spread.
The extent of the damage is hard to measure because the worms do not spread via e-mail, Hypponen said.
Microsoft released the patches Aug. 9. The next day, a Russian individual using the name "Houseofdabus" released working exploit code that could be used to take over machines that have the vulnerability, F-Secure said.
By Sunday, the Zotob.A worm was found. An unknown party had incorporated the Houseofdabus code into a worm that would spread automatically over the Internet, F-Secure said. A similar development occurred in May last year, it noted, when virus writer Sven Jaschan incorporated Houseofdabus' LSASS exploit code into his Sasser worm.
As usual, the worm outbreak kept antivirus vendors working through the night. Hypponen had been up since 2 a.m. and was about to eat for the first time on Wednesday afternoon, he said.
Microsoft's Web page, "What you should know about Zotob," includes links to the patch and was updated Tuesday at
F-Secure has information at http://www.f-secure.com/v-descs/zotob_a.shtml
(Martyn Williams and Robert McMillan contributed to this story.)