Hacking an aircraft single RF system is easy. You just need the appropriate test equipment.
What those scientist did most likely is to synchronize all the different external navigation RF test equipment into a coherent entity and prove they can inject a different navigation signal and fool the aircraft to go where they wanted to.
For this to happen in real life situation with a flying aircraft is something else
All vital systems in any human carrying vehicle (land, sea, and air) should be 100% independent and have absolutely no external connections, such that all interaction must be done with a physical connection and at one single point inside (and under a lock if possible with a real key). This will prevent any external interference through wireless connections. I never believe or trusted any "over the air" updates!
I am tired and frustrated after reading so many "hacking" events since I was a Systems Engineer and a founder of a local ISP, having all the security as my responsibility, too. I changed the password every week, using over 30 character strings and done at the physical site. No one could break it after twenty two years!
Can it be hacked? Is it hooked to Wifi? If so yes.
Even if it is wifi, what is "IT"?
"IT" is pretty much anything with a Wifi connection. Cameras, phones, cars, children's toys, video game systems, refrigerators, you name it. I really did see an article recently that said that cars with Wifi hotspots could be hacked. I think someone tried it on the navigation system of a Chrysler 300 if I remember correctly.
I doubt they hacked into the aircraft itself. Likely they hacked into the communication data link between the airline dispatch office computers and got access to the aircraft's systems. For obvious reasons we will never know how they actually accomplished this alleged hack. Modern airliners and most major airlines have a data link computer that relays flight info every 15 minutes or so to ground dispatch (this is the only reason they were able to narrow down the search territory for Air France Flight 447 that crashed in the Atlantic after departing Brazil). Ground dispatch can also troubleshoot remotely with that access for any problem being reported.
With that said, as a pilot myself, the fact this vulnerability still exists is disturbing. One would hope that disabling the autopilot and taking over manually and even starting to pull circuit breakers for a systems breach would work. But who knows for sure. Target was hacked in a similar "back door" entry matter in that hackers got in through an unsecured HVAC monitoring computer network.
Aircraft have redundant and independent systems between the pilot and copilot displays as well as hydraulic, electrical, and pneumatic systems. So if one fails or is otherwise compromised, another can take over or be switched to the primary system. This needs to happen at the on board computer security level as well.
A lot of higher end commercial engines can be fully computer controlled. If you can get them to go into test mode then you can take full control of just about every system from air/fuel mix, revs, complete shutdowns, hell u can literally play music on some of them by altering rev rates. What this hack was able to achieve l have no idea, but l know what we can do with a ship's engine via a tablet computer over wifi so yeah this is certainly not comforing, especially boings response.