Yeah, ADS-B is going to be the thing. Even right now without wide use of ADS-B you can buy one for under $1,000.00 Soon they will be a $299.00 thing.
Here are a couple: http://www.npr.org/blogs/alltechconsidered/2012/08/16/158758161/could-the-new-air-traffic-control-system-be-hacked http://www.huffingtonpost.com/2012/07/27/hacker-shows-air-traffic-_n_1711343.html
I was really surprised to learn that they are not encrypting these signals. The other story about the Predator Drones not using encrypted video signals make it seem to me that the government does not practice what they preach. They are fast to react when a private sector institution fails at privacy or security matters but lackadaisical in their own endeavors.