When does the hacking start?
Given these things are so hackable, it cannot be beyond the wit of man nor woman in the enemy camp to poison the system with rootkits and trojans during peacetime. If a hot war breaks out, you just fire up your F-35 app and click "ATTACK THE WHITE HOUSE".
Usefully, this technique also applies to autonomous drones and, with a little hooking into a flight sim and Google Maps, even the hijacking of ground-controlled drones.
Now, let me think, who has thriving malware, flight sim and mobile app industries?
And who is not routinely running comprehensive malware checks on their aircraft?