If you ever pay attention to the notices that your PC displays when it's installing updates, you may have noticed references to something called the Malicious Software Removal Tool. This has been part of Windows since Vista, and is designed to detect some of the most well-known instances of malware.
Windows automatically runs the tool regularly on your PC, quietly in the background. Normally you won't notice anything, but you'll get a warning notice if it finds anything suspicious in order that you can take further action.
Although the tool is useful, it doesn't always provide as much protection as it could. You'll only see the warnings about possible malware if you log in as an administrator, and not everyone does that. Also, the tool needs to be updated every month and Windows won't warn you if this fails to happen correctly.
Most crucially, the tool only runs a "quick scan" when it runs automatically in the background. Although it is also capable of running a much longer in-depth scan, this doesn't happen by default.
If you like to ensure that your PC is free of malware, it's a good idea to run the Malicious Software Removal Tool manually on occasion, instead of relying on Windows to take care of things. Running it manually has 2 main advantages. Firstly, it allows you to verify that the tool is up to date. Secondly, you can opt for a full in-depth scan, which will help to detect any hidden malware that has previously been undetected.
To run the tool, use the Windows search box to look for MRT (yes, it's MRT rather than MSRT). Run the command when it appears in the search results. You'll then see a screen from which you can both verify the date it was last updated, and perform an in-depth scan.
[Courtesy of Gizmo's Freeware]