Okay, the other day I was on a web site when this window popped up. I tried to click the red x (never click any part of the box, either yes or no or whatever it says) and it would not leave. I read the box, never clicking anything. It said you need to call this number, your computer has been blocked....blah blah, so I shut off my computer.
The pop up (from what I read) is embedded into the website and you do NOT have a virus and neither does the site. When my laptop booted back up I did a virus check and all was fine. I didn't even need to do a virus scan as I found a great site that explained the scammers try and freak you out and make you think you have something bad on your computer. Once you call them (NEVER call them) they get hold of your computer by remote access and then you have to pay $250 because they hold your computer ransom. This pop is no different than any other obnoxious pop up unless you click on it...
The scary thing is you see this window and it says "just about anything ridiculous such as you have virus or this is the FBI, blah blah. Just remember: IT IS A POP UP! IT is NOT a virus!
People panic and call a number or call Norton or call whomever.
The best thing to do is close out the window and if it prevents you, just manually shut off your computer and restart. Repeat after me. "Toto ....it was only a Pop Up"