SituationWhen browsing, without clicking on anything, the device will suddenly switch to the App Store or Play Store and open the page of a very suspicious-looking app (bingo, in my case).
http://productforums.google.com/d/topic/chrome/EDJTbPaW5dg/discussion this is a long and detailed discussion, with possible explanations, but no definite solution
Where it's been seen by othersSo far, it's reported on iOS and Android. Safari and Chrome. From the second discussion above, someone reported it happening even on airplane mode and blank web pages, which seems like it's burrowed into the browser, not just from ads on a page. Some have associated it with an app, but this isn't consistent.
Where I've seen itOnly on Chrome, iOS, and only when visiting Imgur's mobile site, and only the user submitted section. Oddly appropriate. I haven't tried using Safari to browse that site. Popup blocker was activated (but had m.imgur.com on the allowed list, which is suspicious), but did not help.
On Android, it may be associated with the device, and could be considered a virus (see link in Where it's been seen by others).
VideosI made videos so people know what I'm talking about:
On Safari http://youtu.be/vRkPCdwotRs
On Chrome http://youtu.be/QqwgVHq8UHg