Since most people are going with Iran's side of the story being correct, I'll be the counter voice. It is far more likely that the plane did malfunction and it landed on its own and Iran picked it up. I'm not saying it is impossible for them to hack the communications channel, but is extremely unlikely. Pretend for a second that the military was using something even marginally dumb (which they aren't), the minimum requirement for Iran to take control would be:
* Intercept the control signal
* Decrypt it somehow (in a short period of time)
* Jam (from the ground) the US signal going to the plane, while not jamming themselves (equally unlikely)
* Give the proper C&C commands to the plane to land
Or the more likely scenario of the plane malfunctioned (it is a test plane being used in production) and landed itself.
My biggest concern would be if the self-destructs onboard fired as they were supposed to.
* Intercept the control signal
* Decrypt it somehow (in a short period of time)
* Jam (from the ground) the US signal going to the plane, while not jamming themselves (equally unlikely)
* Give the proper C&C commands to the plane to land
Or the more likely scenario of the plane malfunctioned (it is a test plane being used in production) and landed itself.
My biggest concern would be if the self-destructs onboard fired as they were supposed to.