I tried Avast on my mother's machine, and it got hung up on one particular virus it couldn't erase. Then, after I'd deep-sixed that one, it did it again.

A shame. I suspect it would be helpful in a less toxic environment, though even so, there's no way she'd be able to cope.

(With one thing and another, I took more than 200 nasties off her machine, and I know there were some left, but I just didn't have time. She's got a couple of virus/adware protectors on there now, so at least the rate of infection should have slowed.)