For me, the best antivirus program is NOD32 . It's small (only 7.2 MB) and tremendously efficient. For several times my computer was infected with a virus and neither Norton Antivirus, nor Kaspersky AV couldn't do anything, but NOD32 did a job without any problems. Its graphical interface is not so beautiful and fancy like in some other AV programs (Norton, PC Cilin), but under the surface it's a real beast.

I highly recommend it to all who are primary interested in good and reliable security program, prior to some fancy junk that only look nice but do almost nothing useful (like goddamn Norton AV).