Why is Service Host using so much CPU time?

Ey guys,

I noticed that my computer (running Win7) reacted very slowly. I could see that my CPU was constantly running at 60-70%. So I checked with Process Explorer which process was causing it to slow down. It appeared that a copy of Svchost.exe (or Service Host) was using a lot of CPU performance and I checked what services where hosted by Svchost. It was hosting Windows Defender… Is Windows Defender the cause of my problems? Can I shut this process down?