don’t call the number
Phone scams have been around for years and we are getting smarter about avoiding them. Best just not to answer calls from numbers you don't recognize.
But the in-your-computer scams (usually on Windows computers) are a bit more daunting because you can't ignore them. They might announce themselves as immovable screen graphics, an angry audible voice, or a blaring siren.
Don't panic.
Two things these pop-up scams have in common:
Provide a number for you to call to fix the problem
Warn you against shutting down your computer
My advice:
Do not call the number (I know it looks official, but it's a scam)
Shut down your computer (Hold down the power button on your machine until the screen goes black, then push the power button again to reboot the computer.)
Consider the irony that if you ever needed help from Microsoft and tried to call them, you would find it difficult — if not impossible. So I think there is 0% chance they are calling you out of the blue to help you with your computer. One–to–one help has never been Microsoft's priority.
Please, please, please don't call numbers that appear on your screen unannounced, unless you want to spend the rest of the day on hold waiting for your banks and then changing all your passwords. We have enough other stuff to worry about.