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My computer is trying its best to install this file a security update.
It tries approximately every 10 seconds.
Is this a virus? I've tried google but didn't get much sense.
i'd say that unless you're actually trying to install something, or tried to do so immediately prior to this problem occurring, then i'd treat your machine as infected. what av do you have?
http://www.spywarelib.com/file-0b3558f0c537e16502501b56fa1c4fba-nup.exe.html
Run malware bytes and maybe a anti virus but don't use removal tools on that site.
What makes you think it's a security update? Symptoms? Screenshot?
I'd probably be inclined to System Restore that in the first instance.