Windows Defender is a free program from Microsoft that will protect you against unwanted pop-ups, adware, spyware and other undesired software that will cause your system to run slower and slower. Windows Defender is shipped with Windows Vista, but if you have XP you'll need to download it. Windows Defender keeps itself updated all by itself, and uses the SpyNet community to decide what software should be classified as spyware. You can choose when Windows Defender should run its scan, and the scan works just like a antivirus scan.
