I have had two calls today from people purporting to be from 'Windows Support' telling me that my computer has been sending 'error messages' and is downloading a lot of 'malicous code' and 'spam'. I have not had the patience to string them along to find out what they are trying to do. My guess is that they would try to get me to open a link, log in to my computer and download some malicous code such as a keylogger to detect passwords or bank detauils!
Microsoft do not make unsolicited calls - see their website. In my case I happen to know that I have not bothered to register with Microsoft and so they could not have my phone number.
Do not cooperate with these people! If you have then disconnect from the internet and seek professional help to clean your computer. Run an anti-virus scan. Alert your bank or credit card companies and change passwords and pin numbers if they have had access to your computer.