I had the same experience as MN. He knew my name and was talking about how I needed to update my windows operating system. He had a VERY thick accent, and, since I don't use windows, I hung up. Definitely a scam.
Someone called, claiming that they are calling from Microsoft and that there are some error on my Windows operating system. They will try and walk you through steps to show you that there are errors indeed. Then they will try and ask for a remote session so that they can gain access to your computer remotely. I refused to do so and he threatened that if I don't listen to him he will "cancel my Windows license". They had my cellphone number and used my old hotmail email address which I no longer use.
I'm pretty sure this is a scam. I took my chances and told him that I will deal with it if/when my license is cancelled but I don't want to give him access to my computer.