"(The rate of infection) has remained flat, and we expect it to go down, especially since today is Friday and the weekend is here," Kuo said.
Postini Inc., a Redwood City, Calif.-based security company that cleanses e-mail before it reaches corporate networks, said it had intercepted more than 12.5 million copies of Mydoom and its variant since the original virus was launched on Monday.
In the first 24 hours of the attack, Postini intercepted 3.5 million copies of the virus. On Friday, the company reported an infection rate of 1 in 24 e-mails.
Based on its own customer submissions, security company Symantec Corp., Cupertino, Calif., said Mydoom was spreading on Friday at a rate of 30 percent to 40 percent less than its peak earlier in the week. Mydoom.B, on the other hand, wasn't even on the company's list of top 5 viruses.
Nevertheless, Symantec expected the viruses to continue be a threat for months.