Wonder what the range is. Would you have to be on board the aircraft to hack or would it be accessible through the FAA's net? If its close proximity then it'd be much less concerning to me. Although, hackers are always known to be the brightest with logical decision making (oh, let me crash this airplane I'm in to see if I can do it!).
There has already been a blog written by an actual pilot that pretty much debunks this. This stuff is NOT really serious; it would theoretically work under ideal condition on a simulator, but not so on a plane. People need to take a chill pill.
I wouldn't be quite so quick to dismiss this idea. I think though that as scary as the idea of someone electronically hijacking a plane is, I'm far more concerned about someone applying the same concept to cars. I suspect it's far easier and far more likely. It'll be quite some time before someone convinces me to buy a car with drive by wire tech inside of it.