Windows Defender is an antispyware program from Microsoft that helps protect you from spyware, pop-up windows, and other unwanted software. It's free to download for Windows XP users and it comes with Windows Vista. (You don’t need to download or install it if you have Windows Vista. For more information, see Windows Defender for Windows Vista.)
To check whether Windows Defender is already installed on your computer:
1. Click Start and then click All Programs.
2. Look for Windows Defender in the list presented.
If your computer is running Windows XP and you don't see Windows Defender on the list, you can download the program for no charge.