I don't use an Antivirus. I don't click stupid shit. By this, I'm perfectly safe behind my two firewalls.
Antivirus companies use fear tactics to make you buy their products - did you know that about 75% of viruses are made by antivirus companies? Yeah. Their products of safety download it to your PC then give a big OMFG A VIRUS! GOOD JOB IM HERE TO DELETE IT. DURRHURR.
Seconded @ everyone telling you to get rid of Norton ASAP.
I'm happy with avast! Antivirus, it doesn't lag me or intrude on anything. I haven't needed an antivirus in years, but I'm not such a complete idiot to not have one at all.