The Microsoft Security Response Centre (MSRC) today warns of a new security threat to Windows users.

Hackers are apparently mass-emailing millions of computyer users with a fate notification that includes an executable attachment. Far from being a legitimate MS patch or update, the file is actually a hacker tool known as Backdoor:Win32/Haxdoor. If run by the email recipient, this file installs software on their computer that allows hackers to remotely hijack the system and use it, undetected, as a platform to broadcast spam or to assist in taking over other computers.

MSRC spokesperson Chris Budd assures users that the infection is detected by Windows Defender, the Microsoft Malicious Software Removal Tool (MSRT) and the Windows Live OneCare system. But the best defense is to avoid letting the bug onto your system in the first place.

Late last week, a similar hacker scam surfaced, hiding a system-hijacking download in a fake YouTube notification email.