What's Scareware?
A large amount of attacks on the average computer user is now done in web browsers, attempting to scare users into calling them and getting scammed. It's a very common vector of attack that is really hard to defend against due to the avenue of the web pages generally being through hijacked middle man sites that track browsing data for companies.
Examples:
Web page full screens and start blaring awful noise / warnings telling them to call the number on the screen
Lots of flashing / scrolling text
Very prominent phone number, usually in the middle of the screen
How to counteract these sites:
Use the windows shortcut CTRL+SHIFT+ESC to open task manager, and force close the browser
(If the user doesn't know how to do that, tell them to just reboot the machine real quick)
When you can access the computer, open the browser and check both Extensions and Site settings and permissions, ensure everything is removed if malicious.
Ensure no software on the computer itself could be injecting malicious links into the web browser searches
Another form of scareware is completely based on site permissions, and their ability to push notifications to windows. To get rid of these just clear the site settings in the browser and they will go away.