Get Rid of "YOU HAVE BEEN INFECTED WITH A VIRUS, CALL THIS NUMBER NOW" Completely

I saw a victim of fake tech support posting her mother' s story in Yahoo Answers. Her mother had experienced "YOU HAVE BEEN INFECTED WITH A VIRUS, CALL THIS NUMBER NOW" pop-up scam website and been tricked to call the provided phone number. Then her mother gave the so-called expert access to the computer and paid $200.