I run AV scans from Kaspersky, which I have installed but not running most of the time once every few weeks, at minimum once a month. It hasn't picked up anything in years.
I don't really do torrenting except for the odd TV episode i've missed (i missed house a couple weeks ago as I was out for the evening!), and any other software I don't install updates or new stuff immediately, I learn from Sims.net, always wait a few weeks before installing stuff in case of bugs that break more important things!
Viruses only really come in one way: I've clicked on something I shouldn't have. And nowadays, the most malicious of viruses are these 'fake' virus/AV cleaning ones, which from my experience even the best AV systems don't pickup on.
I teach the staff here if they ever get a window up they don't like/want, and I am not a phonecall away, do not click any grey buttons within it. Click the X's in the corner, press Alt+F4, or simply log off the PC if neither of those are available and they are unsure. Clicking things is what causes viruses!
Lastly, I'm a stay at home nerd who plays one of 2 or 3 MMO's, I have about 12 different password sets, all of which are unique within a set area (So no two Work PW are the same, no two game PW are the same etc etc.) I don't have enough money in an account to worry about, don't own a credit card, and rarely buy stuff over the internet, I'm a cash/card man. I like looking at things before buying, and don't like stuff being delivered if I can avoid it. :)
I'm not 100% safe, but if any of these people REALLY want my credit card details, or my game login's, a simple home AV is not going to stop them if they can still get past a hardware firewall, install a trojan without my knowledge, then run password scanners, steal my email/forum PW, then crack the PW's to my games, and the 4 seperate details/passwords required to get into my online banking