[This version of Windows Defender is still in development, so some Help information might be inaccurate or missing.]

Turn Windows Defender on or off

To complete these steps, you must be logged on as Administrator or be a member of the Administrators group.

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. Windows Defender will also check for new definitions, regularly scan for spyware and other potentially unwanted software, and automatically remove any harmful software that it finds.

To turn Windows Defender on or off

Open Windows Defender. (Click Start, click Programs, and then click Windows Defender.)
Click Tools, and then click General Settings.
Under Protection options, select or clear the Use Windows Defender to help protect my computer check box, and then click Save.