The MS Windows Malicious Software Removal Tool available in 32-bit and 64-bit versions is not an anti-virus application but is intended to detect and remove specific malware such as, Blaster, Sasser and Mydoom. When anti-malware programs are designed for a specific task then the probability of success is much higher than generic programs. The tool removes malicious software from an already-infected computer. Again, this tool is not a replacement for an anti-virus product while Microsoft will be releasing an updated version every month.
This tool works on Windows Vista, Windows 7, Windows XP, Windows 2000, and Windows Server 2003 computers while the x64 version will only run on Vista x64, Windows XP x64 and Windows 2003 x64 computers. Although the tool notifies users (administrator privileges) when they log on to their computer that a malicious program was detected it is worth noting that the tool creates a log file named mrt.log in the %WINDIR%\debug folder.
Note, that all computers with the Automatic Updates feature set to Automatic are getting the latest versions of this tool as soon as they are released. The same tool runs automatically in the background every month and notifies you when an infection is found. However, this process is part of the Automatic Updates feature and hence, is transparent and you can't manage it. Therefore, you need to download this tool from the links provided below to be able to run it whenever you suspect malicious activity on your computer.
To download the 32 bit version go here.
To download the 64 bit version go here.