sorry to hear about your troubles, Peter. Going back to factory settings restored my pc (though it took about 4 days to re-install software and updates) and it was worth it -- no cost to me but time. I still get the pop-up when first booting up but once
I click on the X I am free of the annoyance until next time.
Microsoft did issue a statement about the popup -- they claim it is genuine. Soooo ... the techie you spoke to gave you incorrect advice. It is not a virus.
https://support.microsoft.com/kb/3016799/en-us?wa=wsignin1.0
This being said, I choose not to believe Microsoft -- just stay away from this update. My opinion -- based on my personal experience -- and those of so many others, which date back as far as August 2010.