If you've managed to not know what Windows Defender is, you probably aren't a Windows user. As the not so great security offerings from Microsoft go it's not bad, it does work, it is free and isn't too resource heavy, but nonetheless it is redundant if you have another application installed.

 

Turn Windows Defender on or off

 

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, WindowsDefender will also check for new definitions, regularly scan for spyware and other potentially unwanted software, and automatically remove any detected item that has a recommended removal action.

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 WindowsDefender check box, and then click Save.  If you are prompted for an administrator password or confirmation, type the password or provide confirmation.