As reported by Ars Technica, a prematurely uploaded update for antivirus program BitDefender is breaking 64-bit versions of Windows. The affected operating systems include Windows XP, Vista, and 7. The updated signatures were rolled out to users this past Saturday and began causing false positives (marked as Trojan.FakeAlert.5) on Windows system files, as well as native BitDefender files. The problem pertains to BitDefender Home, Business Client, and Security for File Servers 2008, 2009, and 2010.
BitDefender has since issued a signature update, but unfortunately, those already infected may not even be able to boot up and install the fix. Since BitDefender quarantines infected files, crucial system files have become unavailable, leaving users with rather large paperweights in the shape of computers. For the 2008 version of BitDefender, no fix has been made available. For 2009 and 2010, a user can boot to the BitDefender rescue CD and move the files from the quarantine. In order to avoid a repeat, a user must then ensure that he or she has the latest, working, signature update installed.
Solution guides are provided on the BitDefender website. For those who are unable to solve the problem from the advice given, BitDefender suggests you contact their support team directly.