I received a call from a client recently as he had received a call from a so called "Certified" Microsoft agent, the person calling saying that his computer had errors which is causing their servers problems. You can mostly assume, that any call of this kind from someone or a company you don't know is more than likely a way to extort money from you. They may well ask to get access to you computer and heaven knows what they might do to it if they do.

If in any doubt as to who is calling end the call and DO NOT let them get access to your computer.