I normally would not have answered this call but I was expecting a call from my insurance agent and did not look at the ID. A woman with a thick Indian accent said she was calling from Microsoft support. Microsoft will NEVER call you so I knew it was a scam. Often they want you to give them remote access and will either use it for identity theft or tell you that you have malware and want you to pay to have them remove it. Some will even have you look at info about your system that appears to be errors but are perfectly normal.  Since I despise scammers I began yelling and cursing and it did not take her long to hang up. Here is an article about this scam:
http://www.snopes.com/fraud/telephone/microsoft.asp