I handled the anti-virus software in my computer doing the following:

First I downloaded the anti-virus from this site: {} It was an instantaneous download! (You do not even need to click!)
Then I did not install it, although installing it would have done no harm

Now I had to deal with the real virus, XP annoying me all the time about my anti-virus program which was not recognized, for that I did this:

Control Panel -> Security Center -> Change the way Security Center alerts me -> un-check all... and problem solved, no more annoying warnings

In like 2 or 3 years of running without any anti-virus (I use to run AVG, Lavasoft and the ZoneAlarm for a while) I had 0 viruses, even though I installed software of completely unknown sites, some of them even in chinese making the installation a game of try and catch; but I found out that dealing with a virus once every 10 years (I only got 1 in my more than 20 years of computer use) is much pleasant than dealing with a battery of software that might even behave like a virus. The reason I removed anti-virus, ad-ware and firewall software was that one of those programs was stealing the focus of whatever window I had open, so, if I was typing, all my typing went away to some unknown window, if I was playing the game would minimize if it was a full screen game or just ignore me every 5 minutes of so...

I know the risks, but is a price I am willing to pay for it does really matter little to me, if I need to install XP from scratch, if the problem was caused by a virus or any other software, on the contrary, I rather prefer to install the OS again to remove a nasty virus which I never intended to install instead of chasing a problem for days which eventually leads me to a re-install (like when I had that loss of focus I mentioned), dealing with constants updates (and sometimes reboots), loss of resources, etc all caused by a software that I happily installed.