I encountered a popup similar to this one this morning while checking the weather report at http://touch.woodtv.com/forecast in Safari, though I have not been able to reproduce it.
The title is "about://(null)" and the text "Why you no play Candy Crush!!" The popup occurred twice. I tapped Cancel both times.
I'm wondering if anyone is able to identify the source of the popup definitively. Speculation is running rampant on Apple's support communities and elsewhere, from push notifications (delete Facebook and all your games!) to carrier notifications (which don't work on iPod Touches…), and my gut tells me little of it is helpful. But I could also be very wrong.
(This is not my screenshot; it comes from https://discussions.apple.com/thread/5144627.)
UPDATE 1: The Candy Crush people have this to say, but I'm not (yet) convinced there's actually something installed that is to blame: https://forums.king.com/forum/candy-crush-saga/bugs-known-issues-ccs/recent-spam-why-you-no-play-candy-crush/?entryId=2326
UPDATE 2: Just reproduced it in the iOS Simulator while clicking around woodtv.com, but I'm not sure how to track it down further from here.