When pressing <CTRL>+<ALT>+<DEL> you can find out that svchost.exe process is using up maximum CPU resources and only occurs when Automatic Updates is enabled. Microsoft has recognized this problem and has released a patch. But this patch doesn't guarantee that this problem will be solved.
Open Task Manager and go to "Processes" tab and then press "Mem Usage". If you have this svchost.exe memory leak bug after about 1 minute you will see that the amount of memory usage svchost.exe uses will keep increasing until CPU becomes 99 or 100%.
How to Stop svchost.exe using up 100% system resources (Windows XP only):
1. Download windowsupdateagent30-x86.exe (5.93 mb) and save it onto your PC.
2. Download this file fix_svchost.bat (2.97 kb) (right click and choose save as...) and save it to the same folder.
3. Download this file WindowsXP-KB927891.exe and save it to the same folder.
4. Reboot PC into Safe Mode.
5. Login as an Administrator.
6. Open folder with downloaded files and double click on fix_svchost.bat, do not close the window until operation is finished, it will automatically close itself.
7. Then launch the Windows Update Agent, and simply follow the wizard.
8. Install the Windows XP-KB927891 update.
9. Restart the PC.
10. Check the problem.