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Try Microsoft Security Essentials

Less annoying (no popups)
Less intrusive (doesn't slow down computer like the other 2)
Free (no paid version, all the features are there for free)

Take it to a support center

(do not go to GeekSquad, they are a scam)

Try finding where the program file is and deleting it

Try this article:

How To Format a Hard Drive in Windows XP