Re: Unless you are Really Big Biz this...
Generally Windows Update service for me.
Go to task manager. Right click on the svchost.exe instance consuming all the resources. "Go to Service(s)". If it isn't wuaserv, then I'll be surprised.
You can right click the service and stop it, but it will restart automatically a little later.
As to why it takes so much resource, damned if I know! Perhaps it's another attempt to push us all onto Win10.