An update pushed out on Saturday for the BitDefender anti-virus software will break 64-bit installations of Windows XP, Windows Vista, and Windows 7. The update results in false positive detection of both Windows system files and parts of BitDefender itself. Hundreds of users have been left with non-booting systems as a result.

A new signature update has been published that resolves the problem; anyone still using the signatures from Saturday, March 20 should disable the virus scanning module until the new signatures are installed. For affected users, however, the situation is grim - every file on the system will end up being quarantined, leaving machines unable to boot. To fix affected machines, the preferred solution is to download BitDefender's rescue CD and move the files out of quarantine. If this doesn't work, there are further instructions for BitDefender 2009 and BitDefender 2010 users that should solve the problem. BitDefender 2008, however, has no solution available yet.