I think it is the Safari browser. I had given it up for reading QB, but last night it happened again on another site "LSN", a local buy/sell site. "Congratulations-you've won etc etc. Infuriating! It's driving me to drink!
So I have another browser on my iPad--'Apollo'--it was free from the app store--and I don't have the pop ups with it. I don't know what to do about Safari. Guess I will just kill it and put it out of it's misery!