I've used Avast Free for several years now, & like that it can also monitor email, iweb, and newsgroups (or not, if you so wish, by changing the settings) & it updated right at the startup of my PC. But the most recent version seems to not stay enabled after it booted up, so I relectantly switched to AntiVir for a bit. This one also seemes to work well, except that it wait a while to check for updates & then throws up a big popup screen right when you are in the middle of something. Got rid of it & am currentl usign AVG Free. I have never seen any isssue with resource hits using any of these, & have not had a virus on my PC since the late '90s. My PC is due for an XP "refresh" soon, so I will probably try Avast back again. I'm a little suprised on how many do not use any, but to each their own.