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.