Funny, I just spent two hours the other day at my mothers house fixing her laptop.
Why? Because she got the infamous pop up "Your computer is infected, do not shut down or close this window or you will loose yours files!!!" And of course it had a number to call to remove that nasty virus,,,,,,,..
I found out two days later AFTER she had called the number AFTER she let them on her machine for a few hours to 'clean' her machine AFTER they con'd her into $199 for 1 year warranty on their work.
I had her contact her bank and cancel her credit card. Luckily they caught and stopped the charge from 'James' out of some company in India.
Reason she caught the virus written but the folks who clean viruses,,, my sister updated her to Win 10 and never reinstalled Norton. /facepalm
FWIW, I've always had Java installed (need it for some work I do), never been burnt, never had to reformat a hardrive... Just just gots to not be stupid.
Gee how convenient for this virus warning to pop up AND include a place to call to fix it!!!