I run a savage firewall but I also don't run antivirus. They seem to hand control of your machine over to some 3rd party censor list which you have to trust as much as the files your downloading. They also seem to hose your performance esp when saving and loading from the HDD. I am pretty careful about what I download too and I monitor the processes that are running on my PC fairly well. Its possible that there's stuff running taking barely any CPU and being very well hidden but I am somewhat confident that at the mo there is not.

An antivirus which says that if it doesn't know about something is automatically suspicious is just plain bonkers. For me as a coder I could not write anything under that kind of restriction. I want an antivirus that at most will only flag stuff it knows to be bad. This is just like airport security and the clogging of the people flow through their barriers and has about as much impact on real security too noting the Brinks diamond heist this week which bypassed all security there and had people access a plane baggage hold. Its no difference with files on the drive in this case.