The worm, also known as Nyxem.E, MyWife and Blackworm, is programmed to delete Microsoft Word, Excel, PowerPoint and Adobe PDF files, meaning people should still have about two days to clean up compromised systems. But F-Secure said Tuesday that because the clock time on their PC was wrong, some people had lost important files soon after their systems became infected.
"If you're infected and your clock is not set right, things could start to happen at any time, even though the official activation time is Feb. 3. We've already received first reports from users who've had files on their system overwritten by the worm," Mikko Hypponen, F-Secure's antivirus research director, warned in a blog posting.
All the major antivirus vendors have released patches for the worm, but F-Secure estimated that thousands of PCs have been compromised. The bulk of these machines are thought to be located in India, Turkey and Peru.
Security vendor IronPort has said thatFriday, as the virus will mail copies of itself to contacts in a user's address book.
Graeme Wearden of ZDNet UK reported from London.