Today is Patch Tuesday and while there are a couple of updates scheduled for release later in the day, Microsoft has gone ahead and posted the monthly update to the Malicious Software Removal Tool at the Download Center:

The Microsoft Windows Malicious Software Removal Tool checks Windows Vista, WIndows 7, Windows XP, Windows 2000, and Windows Server 2003 computers for and helps remove infections by specific, prevalent malicious software—including Blaster, Sasser, and Mydoom. When the detection and removal process is complete, the tool displays a report describing the outcome, including which, if any, malicious software was detected and removed. The tool creates a log file named mrt.log in the %WINDIR%\debug folder.

Make sure you download the right system version for your PC:

If you have Automatic Updates turned on then you will get these downloads after they are released to Windows Update although there is no harm in getting updated earlier by downloading them directly.