I can appreciate the value of software that you pay to update you and all, but I've had system-ending viruses with both Norton and McAfee. In the tests I've read Norton, McAfee, and AVG score similarly. In one IW's own Bozos of Bones did, Avast outscored them all. I'm happier with more than one, and even happier to not pay for them
ZoneAlarm must be good though...