In my case...

The update itself triggered at the same time as Norton tried to update itself at the same time that I was using my laptop to take important notes. SVCHOST ate my memory and CPU. The PC froze up and I missed picking up important information - my PC was unusuable.

It was the last act that Norton ever did before being uninstalled forever but I did suspect that Windows Update itself had a hand in matters. Although I'm about to put Kaspersky on instead I am wondering if my PC would perform better and become a useful tool again if riddled with Trojans and security holes compared to the clean unresponsive system it is now.

Many software utility companies (Microsoft included) have forgotten why we wpent hundreds of pounds buying these things in the first place.