Everyone has a different preference for an anti virus, Microsoft windows has its own powerful, and I say powerful defender for virus, malwares, worms ETC. The MSE (Microsoft Security Essential) Comes with windows 7. But if you want to try other antivir program, download free trials first, then upgrade to pro on which ever suits you. Im using Avast free, and its good. Before I use ESET. I dont like Norton because it eats up your RAM and slows CPU. Avira is somehow good but annoying, because of the Pop-up Ad. Mcaffe used to be the best, years ago, I just dont know now. : P But if you really want a no virus OS, well theres only 2 option, getting a MAC PC or getting a LINUX PC ; )