Screen Freeze

[Quincannon]

I use an Apple Mac and opened a website using Safari and after a few seconds the screen froze and a popup message appeared saying it was from applevirusalert.com and to solve the problem I should ring 01158883299 which I did. It was a man with an Indian accent telling me he was from apple mac support and I should follow his instructions.

He wanted me to download TeamViewerQS which made me suspicious so I put the phone down.

The problem is I still can't open Safari because the screen still freezes and I still get the popup I mentoned so can anyone help me please?

I am typing this in Firefox.

Thanks

Peter