My own Dad, an intelligent and computer savvy former medical scientist, fell for one of these scareware scams, and I frequently encounter them in business – usually after a complaint by a client that the anti-virus software I sold them isn’t working. It is, but they have stuffed up their system by downloading malicious software.
Typically, you enter some common search terms into a search engine, and click on an OK looking (in the search engine results) site. This site then loads multiple pop-ups warning your computer is infected with all sorts of dire viruses or spyware. The site tells you you need to download a product which will clean your computer. If you do, and pay the $19.95, or $69.95, or whatever it is, the warnings will dispappear briefly, and then start up again, claiming further downloads are needed.
Don’t fall for this stuff. Get a reliable anti-virus like Norton, Vipre or Kaspersky and update it regularly. Never trust a pop-up that tells you your computer is infected. Just get out of that website, or if you can’t, do a forced shut-down if necessary, then a complete virus scan when you restart.