I got this the other day browsing a torrent site. Hadn't clicked anything, suddenly my monitors all got covered in this warning - pic of a friendly police man with his arms folded and all this text about laws I'd violated including terrorism, violent or sadistic websites and child porn... but if, IF, I was to pay $99 to Nottinghamshire Police and super super promised not to do it again, it'd be viewed as a "caution" and it'd be ok.
What first alerted me to the fact it might be suspicious was that they were asking in dollars. That and the obvious :D
But yeah - I've seen it and that was on Chrome / Win 7.
Reboot fixed it. Scratched that torrent site off my bookmarks.