If a process is allowed to grab 100 percent of CPU time then the operating system itself is fundamentally broken and no amount of fixing the app that grabs that amount of CPU is going to fix the problem. That being said....
Turn off automatic updates. If you can.
You can kill the offending svchost that is running wuauctl that is bogging your system down (sometimes this can take as much as 10 minutes or more on a slower machine) but it will just rerun at some later time putting you right back where you started. Sometimes the task manager will allow you to set the priority of the offending svchost to a lower amount most times it won't it's a crap shoot.
Rebooting will not help you because as soon as you reboot windows will run wuauctl under an svchost and your right back to square one.
or if your paranoid and want those updates
Since the task manager won't even list wuauctl as the culprit as that runs under svchost. Trust me wuauctl is the culprit here.
Get Process Explorer it will show all the running sub process's of a running svchost and will allow you to reset the priority to a lower amount. So....
Get process explorer if you can and set the offending wuauctl process priority to as low as you can set it.
That should net you about 15 to 20 percent of the CPU for the desktop and other apps. About enough
to surf the web but not enough to play a game or do anything else requiring all that much cpu.
Then sit back and enjoy your outdated buggy OS as it updates slowly.