When this occurs, do not call the number on the screen. This is not Microsoft doing this. It often occurs when you click on a corrupted link in the browser or in your email.
You can hit Ctrl+Alt+Del, and that will bring up a menu. Next, select the task manager and make sure to click on the browser program that is at the top, then hit “End Task” to force close the malware pop-up. Afterward, take it to a local tech store to have the computer cleaned up and ensure all traces of the malware are removed from the computer.