If you use Macafee, then you are ok for viruses. You should also have Adaware and Spybot on your machine and run them every day to keep out spies. Finally, you should have Ace Utilities on your machine and run it every day too. It will keep your registry clean and lean and mean.
If you are getting popups about viruses, yes you are being scammed. What you do have is adware on your computer. Try Bazooka Adware and Spyware Scanner v1.13.01 http://www.kephyr.com/spywarescanner/index.html?source=appvisit It sounds like you may have the PurityScan.wtss by clickspring. On my wife's niece's computer it would put up popup ads whenever I put (spybot) in the goggle search engine! The ads were for a $30 program.