The virus, dubbed "Mydoom" and "Novarg" by security experts, started its march late Monday and appeared to be spreading even faster on Tuesday, infecting 1 out of every 9 e-mails, anti-virus software maker Central Command Inc. said.
Rival Network Associates Technology Inc. said the virus had surpassed last August's Sobig.F in the speed with which it traveled, and estimated the latest virus had infected between 100,000 and 300,000 computers.
"It's the fastest spreading e-mail virus ever," Craig Schmugar, virus research manager for Network Associates said. "Sobig.F was out quite a while before it hit its peak numbers, whereas this virus right from the early stages of discovery reached very large volumes of e-mail."
Postini Inc., which cleanses e-mail before it reaches the networks of corporate clients, said it was intercepting 330,000 infected e-mails an hour. As of Monday, the Redwood City, Calif.-based, company had quarantined more than 8 million messages.
By comparison, Postini intercepted 1,400 e-mails infected with Sobig.F on its first day, and 3.5 million the second, Scott Petry, vice president of products and engineering at Postini, said.
The increased traffic from Mydoom hurt overall Internet performance, Keynote Systems Inc. said. The company said its tracking index showed that the Internet at noon Pacific time was 8 percent to 10 percent slower than normal for a Tuesday. Performance, however, was back to normal by 2:30 p.m.
The Mydoom attack appears aimed, in part, at setting up computers for a Feb. 1 attack against the web server of the SCO Group Inc. The company has been the target of several attacks over the last 10 months, with the latest in December taking down the company's server for more than a day.
While not proven, SCO may have been targeted because of its legal challenge of the open-source operating system Linux, which the company claims contains its copyrighted code. SCO's lawsuits have angered the Linux community and its supporters. Conversely, Linux enthusiasts say the virus may have been assembled for the purpose of defaming Linux developers.
On Tuesday, SCO offered a $250,000 reward for the arrest and conviction of the Mydoom virus author.
"The perpetrator of this virus is attacking SCO, but hurting many others at the same time," Darl McBride, president and chief executive of SCO, said in a statement. "We do not know the origins or reasons for this attack, although we have our suspicions. This is criminal activity and it must be stopped."
SCO is working with the U.S. Secret Service and Federal Bureau of Investigation in investigating the virus.
While security companies rated Mydoom near, or at, the top of their rankings in severity, some disagreed as to the speed with which the virus was spreading.
Based on customer submissions of virus-infected e-mails, Symantec Corp., which ranked Mydoom a level 4, with 5 being the highest rating, placed the virus on par with BugBear, a mass-mailing worm that struck in 2002, but did not proliferate as fast as Sobig.F. As of mid-afternoon Tuesday, Symantec was receiving about 150 submissions of Mydoom-infected e-mails an hour, with about 9 percent from corporate customers.
"It hasn't tapered off, which is rather unusual," Alfred Huger, senior director of engineering at Symantec, said. "That means this virus hasn't reached saturation, yet."
The virus, however, was expected to taper off over the next 24 hours, Huger said.
"Mydoom" arrives in a zip file carried in an e-mail with the subject lines "test," "mail delivery system," or "mail transaction failed." The body of the e-mail tries to trick the receiver into thinking that the actual message is in the attachment. The message contains such statements as "The message contain Unicode characters and has been sent as a binary attachment."
Once opened, the worm installs a program in the infected PC and opens a "backdoor" that enables a hacker to take control of the computer, apparently in preparation to flood the SCO server with information Feb. 1, security experts said. The kill date for the worm is Feb. 12.
The virus, which affects computers running Windows 95, 98, ME, NT, 2000 and XP, scours the infected computer's hard drive for e-mail addresses to send copies of itself. Mydoom also copies itself to the download directory on PCs for the file-sharing service Kazaa.
Symantec's Huger said the company had received unsubstantiated reports that spammers were already using infected machines to send spam. Technologically savvy spammers can sometimes piggyback on the malevolent code sent by others.
Several companies reported battling the virus, but did not suffer any severe damages. The Boeing Co. in Chicago told the Wall Street Journal Online that the virus clogged its system to the point where employees were unable to use e-mail Monday afternoon. The online news service also said Xerox Corp., Cisco Systems Inc. and Lehman Brothers Holdings Inc. had fended off attacks.