A new version of MyDoom uses an unpatched flaw in Microsoft's Internet Explorer to spread, antivirus companies warned on Monday.
The recently discovered vulnerability in the browser software allows the offshoot to infect a PC after a user clicks on a link, according to advisories from security software makers Symantec and McAfee. The program sneaks past antivirus applications that detect malicious software by scanning e-mail messages with attached programs.
The companies said they had only detected a few instances of the infector, which is labelled MyDoom.AG by McAfee and MyDoom.AH by Symantec.
"We have only received one submission from the field, but the technical aspects of this are concerning," said Craig Schmugar, senior virus research manager at McAfee. "It has all the components there to become a significant virus."