I use Symantec AntiVirus, the bad side with it is that I always have to keep updating it manually.
Positive thing is... I don't know what the programme really does. So I don't really feel safe with this anti-virus. I'd recommend kaspersky, I used it before and it stops all viruses, trojans, worms, adware, spyware and other malicious software, and it prevents keyloggers.