If you have ever tried to contact Microsoft for help; you know it can be a difficult process. So if you ever out of the blue get a message from someone claiming to be Microsoft while telling you there is a problem THERE IS!! You have been infected by them and they want your money. NEVER let anyone that you do not know access your computer remotely. I see this infection about ten time a week. It usually has an 800 number to call as well as someone repeating that you are infested.
If you know a lot about computers you may be able to deal with it yourself. If not just turn it off and call a technician. There are many forms of this malware and they look legitimate. I would like to give you some direction but because this is a nasty piece of malware you could make things worse. If you have some program designed to remove malware you might try running a scan. I like to use malwarebytes http://www.malwarebytes.com