There is an ongoing outbreak of unsolicited support calls, purporting to be from Microsoft, or some other company on their behalf, offering Windows support. They often claim that your computer has a virus or is running slowly.
These calls are not genuine, even if they are able to identify you by name and location. The whole purpose of these calls is more than likely to infect your system with various kinds of malware.
The most important thing is that you do not follow on your computer any of the instructions they try to give you.
If you are called at home with one of these calls, it is best to ask for details of the problem so that you can ask your engineer to take a look at it. This will normally either totally baffle them or make them very angry. Alternatively you could simply tell them you are wise to this scam and that they should stop calling.
Of course, if you have a computer running something other than Microsoft Windows, you could always try to waste their time... if you have time to.
If you get one of these calls at work, ask for the name of the person calling you. If your employer's IT section uses any kind of ticketing system, also ask for the ticket number. Then tell them that you will call back. Do not use a number they give, or one they try to offer. If the call even gets to this point, I would be surprised, but hang up, and call your local IT section on their usual number. If the call was genuine, they will be able to put you through to the right person. If the call was not genuine (the most likely scenario), your IT section will be pleased that you handled the matter correctly, and may also remind the rest of the staff that this is still ongoing.