That sounds like the source of the problem right there, a lot of things can go screwy when updates or other installations occur during a virus scan. I myself screwed up by running a virus scanner and a defrag at the same time
.
Since that may be the problem go to
update.microsoft.com and download the latest updates to see if that cures the issue.
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"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
~Albert Einstein