Isn't this exactly the kind of thing Apple's app approval policy is supposed to protect against?
It would be very difficult for Apple to check for this sort of thing. This is not Apple's responsibility IMO.
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Edit: And by very difficult I mean the simple case is easy to catch, sure, but encryption makes that tougher. On top of that, one could easily make it a "Time Bomb" such that it were delayed by some set time or remotely activated after approval. I think the responsibility for this should go right to the dev. If it's against Apple's rules then they should pull those apps from the store.
