1. Open Windows Defender by clicking the Start button , clicking All Programs, and then clicking Windows Defender.

2. Click Tools, and then click Options.

3. Under Administrator options, select or clear the Use Windows Defender check box, and then click Save.
If you are prompted for an administrator password or confirmation, type the password or provide confirmation.

When Windows Defender is on, you will be alerted when spyware and other potentially unwanted software tries to install itself, run on your computer, or change important Windows settings. If you use the default settings, Windows Defender will also check for new definitions, regularly scan for spyware and other potentially unwanted software, and automatically remove any malicious software that it finds.