Disclaimer - I don't know how they do this on newer networked aircraft like the 787, but the systems on the 737, 747, 757, and 767 use ARINC 429 ONE WAY data busses to communicate aircraft information to the IFE. I'm repeating myself (again), but ARINC 429 is effectively hack proof because it's one-way (so it's impossible to corrupt the source from the destination), and you need a physical connection to put data on the bus.
The most a hacker could hope to due via the IFE would be to take down the ARINC 429 data bus.
Just one of the many things that make the hacking claims so laughably fake...