that also depends on how much money your going to spend....

free AV programs are various and easily found.... as are 'online' scanners... also what OS are you using?? i'll assume windows for now... and because your asking i will just quickly say (and i might be wrong, someone back me up or otherwise...) to use Nortons AV if you want to buy it.. otherwise AVG is on the web somewhere.... like here.... www.grisoft.com

personally i would choose Nortons over McAfee... buts thats just one mans opinion