Stopping pop up saying virus?

[countmypennies]

I have one system windows 7 that is more open to the outside world because of the user that needs it, and he still gets that damn pop up once a week telling him "message popup saying i have virus and windows is damaged" it s when he goes to yahoo or msn homepage. He either has to restart the system but now hits ALT=F4 which closes it. the pop up blocker is on. Can i disable a feature to stop this from occurring although he does use some pop up windows and features in business. ?

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[samuria]

What browser most can run in a type of safe mode disabling extension etc see if that stops it if it does it's an add-on giving the problem. It could be a schedule running

 

[countmypennies]

What browser most can run in a type of safe mode disabling extension etc see if that stops it if it does it's an add-on giving the problem. It could be a schedule running

What?