The "PORNOGRAPHIC VIRUS ALERT FROM MICROSOFT" scam is a simplistic, low-effort tech support scam that tries to lure its victims into calling a fake technical support number. The alert appears as a plain browser pop-up window with just text in it. The bad actors behind the scam use social engineering and common scare tactics to urge their victims into calling the fake support number. Dropping Microsoft's name in the fake warning attempts to give the fake alert some credibility but on the other hand, undermines the entire affair because Microsoft will never "lock" your computer or send a "notice" to your address for failing to call their support lines.
Here is the full text of the support scam's pop-up:
PORNOGRAPHIC VIRUS ALERT FROM MICROSOFT
This computer has been LOCKED
Do not close this window or restart your computer without calling support
We have locked this computer for your security
You have been browsing unsafe pornographic websites.
Your computer has been infected.
Contact the Microsoft helpline to reactivate your computer.
Failure to call will result in a notice being sent to your residence.
Bad redirects will drop unsuspecting users on malicious pages that bring up the support scam pop-up and that are designed in a subdued blue-and-white color scheme that attempts to mimic that of Microsoft's official Windows-related pages. There is no reason to call the listed support phone as it is neither associated with Microsoft in any way nor will it provide any answers or fixes, because there is no "pornographic virus" on the system. The only issue here is the fake pop-up itself and the malicious websites that generate it.
It's likely that the scam pop-up caused the system no harm and was just a minimum-effort attempt to scare the victim into dialing a pay per call number. Regardless, the best solution, in this case, is to navigate away from the browser tab that caused the fake warning, close the browser and then run a full system scan with a reliable anti-malware suite. A manual sweep of any newly appearing suspicious browser add-ons and their removal is also recommended.