Last week Microsoft released (or perhaps I should say re-released) a beta version of Windows Defender Offline, a seriously useful tool for recovering dead Windows XP (SP3), Vista (RTM, SP1, SP2), Windows 7 (RTM, SP1), or Windows 8 (Developer Preview) systems. Yes, it even works on Windows 8.
Curiously, except for the Windows 8 support, it's almost identical to the old Microsoft Standalone System Sweeper.
Windows Defender Offline is designed to be used when you can't boot an infected PC. You create a Windows Defender Offline USB drive, CD or DVD, or ISO file, then boot from the Windows Defender Offline device. Windows Defender Offline performs a scan based on its stored signature files. Since you're not booting to the copy of Windows installed on your PC, Windows Defender Offline stands a fighting chance at identifying rootkits and other malware that fly underneath the operating system radar.
Acquiring Windows Defender Offline is a three-step process. First, you download and run an installer/updater. You're given a choice between 32- and 64-bit versions; choose the bit count matching that of the PC you're trying to fix, not the one that's doing the downloading and installing.
Next, run the installer/updater to create a bootable USB drive, CD or DVD, or bootable ISO image. If the USB drive already has Windows Defender Offline installed, running the installer/updater will update its signature files. If it doesn't already have Windows Defender Offline installed, the USB drive, CD, or DVD is reformatted prior to installing Windows Defender Offline.
Finally, you boot to Windows Defender Offline on the afflicted PC. If you have a multiboot system, you must choose one of the OSes; Windows Defender Offline will scan only one system at a time. Windows Defender Offline takes over, giving you the opportunity to run a quick, full, or custom scan. Much like Microsoft Security Essentials, tabs on the interface let you update the signature files, look at the scan history, or exclude specific files or folders. In my tests, it took about 20 minutes to run a full scan on a Windows 8 Developer Preview machine.
The PC you use to install Windows Defender Offline must be connected to the Internet. The PC you scan need not be connected.