I received a call purporting to be from Microsoft windows explaining that my laptop was infected with many viruses. I am an internet/laptop virgin.

I was shown evidence of my "infection". I asked how this could be as I have protection and was told that as everything was infected my anti virus could no longer recognise any threats and Microsoft windows could fix it for me. They managed to get mu IP address from me and proceeded to remotely "fix" my problems. After quite some time (over an hour) a price list was displayed to me the cheapest anti virus being £108 which I could not afford. I was asked if I could afford £50 and by now was smelling a rat (I'm slow on the up take) Now I am worried sick because they accessed my computer and I don't know if my security is compromised. I don't know what steps to take to check this and to add insult to injury they have rung me back twice since this happened yesterday telling me that my computer is going to shut down any time soon with no chance of recovery. I hope some-one can help me.