The beta tool allows users to create a recovery CD/DVD or USB stick and use it to boot Windows. It comes with the virus definitions, which allows users to clean their system even when it is dead.
Apparently the tool has a greater chance of discovering and removing malware because users are not running the software through the infected Windows platform installed in their PC, but rather through a recovery disk. The tool supports Windows XP Service Pack 3, Windows Vista Service Pack 1 and 2 and Windows 7 Service Pack 1. The tool also supports the developer preview version of Windows 8.
According to its Windows Defender Offline page the Windows Defender Offline Beta can detect malicious and potentially unwanted software, and then notify you of the risks.