avast is good in (on-demand scanning ) but not at the real time protection ..
I recommend you to try the free version before you make the buying move ...

I started using the free version when my McAfee subscription expired after it had given me repeated trouble with the infamoun black M problem.

First thing after I loaded it, it ran a scan and immediately found several virus files that McAfee had missed.

I find it easier to use and it uses up less memory.

ive said it in another post, but i use and recommend avast on all of my customers computers and my own.
Ive seen people using AVG and other free and pay AV progs, phone me up asking me to come round and do some work on their bugged out pc.

So i just slap avast on there and depending on the size of the hard drive, im done in less than 2 hours with a nice clean pc.

Only problem is that i never get antivirus work off these customers again, cos avast does its job so well.

On further ways of staying safe in the world wide jungle, try out sandboxie. Ive tested it by actively looking for really dodgy sites and getting my pc infected , but sandboxie is one hell of a program. I wont say anymore, just suggest you try it out for some extra surfing safety.

The URL is:Sandboxie - Front Page

anyways have a good one.