100% SCAM
They are NOT from Microsoft - Microsoft does not call you. How would Microsoft know your phone number to begin with?
This scam is going around and they pretend to be from Dell, Microsoft, Norton, various ISPs, etc. It's a scam that has 2 parts
1- they want you to log on to a remote access site so they can INSTALL a virus/malware on your computer, not get rid of it. Then they will blackmail you into payin up to $1500 to remove it
2 - While they are on the remote access site, they are copying ALL of your files - your passwords, Contact lists, documents, banking info, etc for future identity theft purposes and hacking into your accounts to steal your money
If this person calls again, hang up then immediatley call your phone company to ask for the number the last call came from. Then file a police report