Windows Defender Service is using high CPU all the time. What can I do about this?

Last week Windows Defender detected a Trojan in my system and since then, even after removing the threat, the Windows Defender Service constantly uses about 20% of my CPU. There's no clear indication as to why it is doing this. This is really annoying since the high CPU load triggers the loud fan to be active on my DELL XPS 502x laptop. I can't hear myself think basically. Is there any way to reset Windows Defender somehow? Reinstalling it perhaps?

Ans
1.

Windows key + X and select Command Prompt (Admin) and type sfc /scannow and return.  If it repairs system files, run it again until no errors.

In case Windows Defender is caught in a loop, consider running it offline per the following tutorial..

http://www.sevenforums.com/tutorials/166445-windows-defender-offline.html

If this does not solve your problem, restore the default settings of Windows Defender Services only per the following tutorial

http://www.eightforums.com/tutorials/9413-services-restore-default-services-windows-8-a.html

If the problem still persists, you may have to Refresh Win 8.