avast is not what I recomend to my customers. When I see norton on a machine, i just laff.
Meowzer, if you have the time in the morning, go through this and yes its free ->
http://www.bitdefender.com/scanner/online/free.html
If you have anything bad, it will catch it and remove it. If you are going to purchase anti virus software, i only recomend panda. Nothing else is really close to it other than NOD32 but that was a while ago. I know panda is still good.
Myself, I have nothing installed AV wise on my machine and I dont need to. The last virus I had came from my wife browsing through facebook. that site is now banned in this house and since then, all clean. Its not about what OS you use, its more about where you go on the internet and what you are looking for. Yea, since we had this machine, about 9 years, i have only used the AV that came with the machine and when the "trial" period expired, I uninstalled the software and never installed anything. I am a more advanced PC user than most, 8 certifications, but the general rule applies. Dont look at pron, stay away from the silly game sites, dont DL anything you are half way unsure of, and be smart.