What’s different about the version of Windows Defender that comes with Windows 7?
In Windows 7, Windows Defender has simpler notifications, more scanning options, and less impact on your computer's performance. A new feature called "Clean System" provides one-click purging of all suspicious software. Windows Defender is also now part of Action Center, the new, streamlined place for keeping your PC running smoothly. All notifications from Windows Defender come through Action Center.
You can also use Autoruns for Windows to stop a program from running automatically when Windows starts by clearing the check box next to the name of the program. Autoruns for Windows is designed for advanced users