I experienced a strange error with Windows Update and Exchange 2007 AntiSpam updates on Windows Server 2008. When I enabled Exchange AntiSpam updates Windows Update would never stop looking for updates. The host process for Windows Update, Svchost.exe, would run at 100% of one CPU core and never stop. I had to kill the process in Task Manager. It was like there was an infinite loop condition somewhere in the code. When I disabled AntiSpam updates in Exchange Windows Update functioned properly again.
The root cause of the problem was Windows Update and Microsoft Update. To fix issue I had to disable and re-enable antispam updates. This can be done by opening the Exchange Management Shell and run:
Enable-AntiSpamUpdates -Identity <mail server> -IPReputationUpdatesEnabled $true -UpdateMode Automatic -SpamSignatureUpdatesEnabled $True
Next, I had to reinstall the Windows Update and Microsoft Update components. Open up a command prompt and run:
net stop wuauserv
ren SoftwareDistribution SoftwareDistribution.old
net start wuauserv
Finally just manually run Windows Update and re-enroll in Microsoft Update again and everything should now work properly.