Microsoft Security Scanner

Microsoft has released a no-nonsense simple to use, free and downloadable tool – Microsoft Security Scanner – to check and cleanup virus infections (or suspected infections).

This tool is not intended as an antivirus, it is intended as a cleanup utility for infected computers or as a tool you can download and do a double-check to confirm you are not infected (say your installed antivirus is unable to detect a certain virus/malware, then you can double check using Microsoft Security Scanner).

You can download it free from here (note the download only works for 10 days, then you have to re-download an updated version, this is to ensure the virus detection patterns are always fully up to date);
http://www.microsoft.com/security/scanner/en-us/default.aspx

A good thing to also do is to run Microsoft Malicious Software Removal Tool from time to time – this is done automatically as part of  Windows Update, however this is only the ‘fast/quick’ scan – by starting the MRT.EXE manually you can do a FULL scan.  The Malicious Software Removal Tool is installed on all windows machines and updated/maintained via Windows Updates.

to run it;

Btw; McAfee has  a similar yet not so comprehensive utility called Stinger (also free download);
http://www.mcafee.com/us/downloads/free-tools/stinger.aspx