Even with the appropriate security measures in place, there is always the possibility that an instance of malware can go undetected by your anti-virus software or even disable it. Microsoft designed the Malicious Software Removal Tool for such situations. When the tool runs, it detects and removes any malicious software it finds on your computer.
Although the tool is not necessary if you are running up-to-date anti-virus software, it does provide another layer of protection. The tool is installed with Vista and is available as a free download for Windows XP. You can locate the tool by typing mrt.exe in the Search field on the Start menu.
When the tool runs, you can choose the type of scan to perform. You can perform a Quick, Full or Custom scan. If you choose a Quick scan, the Malicious Software Removal Tool will scan the areas of a computer that are likely to contain malicious software. A Full scan checks the entire system for malware. You should perform a Full scan occasionally but be advised that it can take up to a few hours depending on your system.
Finally, you can opt to perform a Custom scan and choose the folders or areas of your computer that you want the Malicious Software Removal Tool to scan. The results of the scan indicate whether any malicious software is on your computer.