A virus that travels via e-mail and attacks Windows operating systems was first noticed on September 30th and has already infected computers in dozens of countries. The bug has been aptly dubbed Bugbear. It is rated "high risk" for both home and corporate users.

Bugbear arrives as a worm embedded in an attachment to an e-mail. But users don't need to open the attachment to release the worm. Merely opening or previewing the e-mail can allow the bug to infect a system. Among the subject lines reported to date are: "Just a reminder," "News," "Membership Confirmation," "Market Update Report" and "Your Gift."

This virus spreads by e-mailing itself to addresses found on the user's machine or attaching itself to previously sent e-mail messages. It also attempts to disable many types of protection, including antivirus protection. Some reports say that after Bugbear infects a system it sends print requests to all network printers.

If it succeeds in infecting a computer, Bugbear can allow hackers to delete or steal any information stored on the computer's hard drive. It attempts to install a backdoor trojan that can record user keystrokes, including passwords and credit card numbers. It can also enable a hacker to download files onto an infected system, stop processes from operating and run executable files.

Microsoft has issued a patch for the problem, and both McAfee and Symantec have released information about and fixes for the worm. According to the MessageLabs VirusEye chart of the top 10 viruses, which tracks computer infections on a daily basis, the Bugbear worm is attacking more than twice as many systems as the Klez worm, this year's previous greatest threat.