XP Windows using Automatic Updates
SVCHOST.EXE runs at 100% CPU (Single Core) or 50% (Dual Core)
Microsoft have stated this is a known bug and they are attempting to fix it – Until this bug is fixed you either need to disable Automatic Updates via the icon in the Control Panel or manually download and install the current Cumulative Security Update for Internet Explorer. The Automatic Updates process uses the Internet Explorer engine even if you have a different default browser installed.
Check this news article:
This issue comes about because Windows Update is heavily reliant on components of Internet Explorer. If these components are not up-to-date, later versions of Windows Update Agent (that’s the engine that scans for and manages updates) may fail or exhibit very poor performance.
It is NOT necessary to install a new version of Internet Explorer to resolve this issue. What is actually required is to install the latest cumulative security update for whatever version of Internet Explorer you have installed. This will be IE6, IE7, or IE8 (if you’re doing a fresh install of Windows XP it will naturally be IE6). This will upgrade the various components of your Internet Explorer installation. Thereafter Windows Update will perform as it should.
The secret is to install the LATEST Cumulative Security Update for your version of Internet Explorer.
This is a recurring problem so the current latest versions keep getting updated each month.
A Google search will find the latest: Cumulative+Security+Update+for+Internet+Explorer
The latest updates are dated November 2013 (as of writing this). Download and install the update that corresponds with your currently installed version of Internet Explorer: