A iPhone Hardware Implant Discovered in Russia
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The reporter mentions that the circuit board touches the display and that it must somehow be able to monitor what's being displayed on it but I think he is mistaken given how difficult the task is (this would be a Tempest-style attack: https://en.wikipedia.org/wiki/Tempest_(codename) - why bother when you could just hook into the display connector and get the data out of there?).
In short it seems to be a microphone bug + GPS tracker, all powered off the iPhone's original battery (so that it's essentially always on as long as you keep your phone charged) but it doesn't seem to be accessing the iPhone's data or compromising its operation in any way.