Something very similar, not quite the same ad, has happened to me a couple of times on the retrorides boards today. They're on the proboards forum system.
If you're on an HTC, you can stop the redirect when the page is loading by pressing the X next to the address bar, or if you miss that, you can press the 'search' magnifying glass to take you to google, avoiding the popup without task manager.
Following these most recent posts, I am resisting my usual habit of looking on PH on my mobile in bed during the daily lay-in. Ta to the administrators for the continued efforts.