I have no anti-virus installed and have never needed one (well, not since I was 12), and this is even with the tons of cracks etc. I go through for gaming.
As long as you download from a trustable source and not some random torrents found using google, you'll be safe mostly. Out of interest I ran several AVs around 3 years after I last reinstalled XP on my older PC, nothing detected except the usual internet explorer cookies (which I don't use either way).
If you feel you don't need an A/V then don't use one, if you feel you need one then get one simple as that.
this is just like saying i leave the backdoor to my house unlocked and i have never been burgled
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Out of interest I ran several AVs around 3 years after I last reinstalled XP on my older PC, nothing detected except the usual internet explorer cookies (which I don't use either way).
I've heard that outbound protection is pointless because anything already on the inside can compromise the firewall but it's worked well for me so far. Anything that is vicious enough to cripple the firewall I'm hoping I'm not dumb enough to let in or that the AV gets round to doing some work and catches it.
Just install Microsoft Security Essentials to be safe.