He's talking about a "payload" (think "virus") that could be deployed on the FMS computer. I've no idea how (or if) this can be done, but if it could then it should be relatively easy to modify the FMS's inputs so as to deliver the desired outputs.
While ACARS/ADSB normally have no connection with the flight controls, my understanding is that this connection is precisely what this "payload" provides. But it doesn't have to - it may just contain the instruction to fly into the ground on the 4th of July, for example. Of course, that wouldn't be as cool as controlling the plane through your Android phone.
The real challenge isn't in programming the payload, it's in delivering it (or preventing its delivery, depending on your point of view). One hopes that the security measures involved with program updates (and possibly also nav data) are up to the task.
It's been done with industrial control systems (stuxnet), no fundamental reason why it can't be done with an FMC.
Last edited by fizz57; 11th Apr 2013 at 07:30.