The 1st AV i ever used was Norton, it was very good, did its job and never has a problem with it, but in the end it was slowing the system down and using a lot of memory, so i then changed to AVG, avg was good, but didn't have a lot of feature like Norton did, didn't have a auto notification saying that something was blocked or attempted to access the system, you had to manually scan and didn't have a anti spy ware integrated at the time, so then i tried Nod32, was much better than AVG, did its job provided information is something bad cam through and gave me the option on what to do, in the end NOD32 killed my system completely, due to some TCP stack issue, reformatted winxp, then game kerpasky a whirl, using only the trial that they had going, it worked but felt like it wasn't informing me what was going on, only saying that things were blocked and that was pretty much it, and sometime getting the occasional pop up trying to get me to update to a paid version, eventually i got rid of kasp, then recently i moved onto Avira, no problems with avira at all, only thing is it doesnt provide real time background support, and anti-spy integrated, it would only sometime report a problem, i also had a root kit and it detected it, but wouldn't remove it at all, lucky i knew how they worked and just got rid of it manually, but at least it detected it, avira was fine but just wasn't enough for me, and now I'm using avast, remembering that one of my good friends uses avast and they haven't had a problem with it, thought that i should give it a go, so far so good, Tells me when its updated itself , notifies me if something bad attempted to get into my system but blocked it, also blocks any incoming attacks on the network. so far its doing its job and notifying me on what going on, and has anti-spy built it, and has real time background running. I've only used Freeware Anti-virus applications also, in the exception to Norton witch was my only paid service.