What is svchost.exe?
According to
this Microsoft KB, svchost checks the registry while your computer is starting to see which services it must load and then loads them. It often appears in the Task Manager multiple times, as it groups those services together. This is perfectly normal and safe.
Why is it using 100% of my CPU cycle?
There can be multiple causes, but most often is due to malware or a service that is not working properly.
How can I fix it?
First, make sure your computer is free of malware. There are several sites that let you scan and remove malware for free, and many of the forums in my "Helpful Links" page have malware-removal experts who can assist you.
If you computer is malware-free:
1. If this just started recently, try a System Restore.
2. Go to Start | Run and type %systemroot%\system32\restore\rstrui.exe
3. This will bring up System Restore, and try to choose a Restore Point from before this started.
If that doesn't work, then try the following:
1. Download Sysinternal's extremely useful Process Explorer
2. Read the license terms and click that you Agree (if you do)
3. Look at the list of processes and see which particular svchost.exe is the culprit.
4. Once you have determined that, double-click the svchost.exe and go to the "Services" tab
5. It will list the services that are running.
6. Look up each service on Google, and if it is not necessary, stop it, then see if the problem stops. Then, once you know the service, research it further and determine whether or not it is necessary for the safe operation of your computer. You can disable the service by:
Start | Run and type services.msc
Find the service, right-click it and click Properties
Then, change the startup type to manual or disabled
If it is necessary, try to research the problem on Google or another search engine and see if there are any suggestions.
If you need help, there are several links to tech support forums on the Helpful Links page.
Automatic Updates is the cause. What should I do now?
Update: Microsoft, of course, is working hard at fixing this issue. There are updated instructions here at the WSUS product team blog.
It seems that quite a large number of people are having this problem recently. Microsoft's suggested fix is to download the hotfix here and to update the Windows Update Agent and has instructions and a download link here.
However, this does not seem to work all of the time. So, to at least allow you to temporarily use your computer you can disable the service. Please watch for a fix or update from Microsoft so you can enable Automatic Updates again. This fix is only temporary and should be reversed as soon as possible.
You can disable the service by:
Start | Run and type services.msc
Find "Automatic Updates", right-click it and click Properties
Then, stop the service and change the startup type to disabled
To re-enable it, click to see its Properties windows and change the startup type to Automatic.