help with invasive software

First off, I have three avast subscriptions between all of the computers in my house. I am usually happy with your software (it finds the virus and takes care of it). I don’t understand this problem though. The kids have gotten this twice before. One computer is still up and running, I got rid of it accidentally experimenting. The other one is down, although I doubt if this problem had anything to do with HD going down. They both got the problem when their av protection expired, not telling me, and was on the internet without protection.

What slays me is that Avast doesn’t detect it, even the full deep scan.

It will flash a message on the screen saying that the computer is infected. It has a red shield like it is a defender of some kind. My son clicks on the “remove virus”, and it pops up a screen wanting you to buy virus protection. I already have avast so I tell him to x out of it. It keeps coming back. Won’t go away.

Can you tell me what it is, and how to get rid of it for good?

Thank you
klf

this looks like a rouge whts its name?

anyway download malwarebytes from here:

http://download.cnet.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html

do a full scan and remove whatever it finds post logs on next comment and tell me whether this was helpful or not?

Thank you, I will try that when my son and his laptop come home. He said it was still doing it even after the full scan. This is the second time I have encountered this virus (?). Last time I tried all kinds of fixes, still don’t really know what I did to make it go away, and this is a brand new laptop. Don’t want to screw it up. Know enough to make me dangerous. I want to fix it the right way. I will touch base when I try what you suggessted. Thanks again.