Security At Home:
The technology behind Windows Defender, Microsoft’s popular antispyware software, is built into the Windows Live OneCare online safety and security software subscription service. If you use OneCare, you do not need to download Windows Defender.
If you already have Windows Defender installed on your computer, and then you download Windows Live OneCare, you do not need to uninstall Windows Defender. OneCare will automatically turn off Windows Defender so you won’t get messages from two different versions of the program.