There seems to be a lot of large attention getting messages popping up on our PCs claiming that our machine is infected and to call Microsoft at some number to fix. It appears quite often when people are using social media such as Facebook (and has appeared on my PC also) and is probably with one of those posts that does some type auto play.
If it pops up on your screen first know it is not from Microsoft but some spammer or other threat actor. Calling the number that says is Microsoft will get you someone claiming to be Microsoft (but are lying) and who will want personal information from you and then credit card or bank account information that they will then either tell you how to clean your machine or they will want to access your machine to clean it. Now they have your financial information and they can go do lots shopping on you. If they send or load a program on your machine they say will clean, be aware it actually does the opposite and will load your machine with viruses and spyware, etc.
If you do give them any account information, immediately when you hang up (or if you already did and reading this, immediately now) call the credit card company or the bank you gave the person at “Microsoft” your account numbers and report it so they can freeze your account or watch very closely. Most experts also advise filing a police report, although they will not be able to catch them most likely as likely in another country. However the financial institutions like them to build cases.
Next whether you called them or not I would advise doing the following. First run a full virus scan on your computer with your anti-virus software. If it occurred on your phone do the same. There are a number of good free anti-virus programs for your phone. My current preference is for Avast and is on my PC, laptop and phone. That will catch the viruses, just to be extra safe you may want to do a boot anti-virus scan, just be aware it may keep you from being able to use the PC several hours so I usually do that overnight. The anti-virus programs try to spot spyware also however I find that is not what they are best at. There are several anti-spyware programs available and if you do not have one install and run scan. If you do have one, run a full scan. My preference is for superantispyware.com which is free although I have professional on two machines as it is cheap and can be installed on several machines.
Back to auto play. I wish Facebook would disable that feature as it is very irritating and depending on where you are when you access Facebook can be a problem. In the late 90s that was done a lot on web pages and then people figured out it irritates and they quit putting there. The only reason I can think of why appearing again is it has been 20 years, and a new generation is on Facebook and they are proving the statement true ”Those who do not know history will repeat it”