Hacking an Airliner?

Hacking is in the news a lot these days, not surprising that it makes its way to tv drama . question in this case is how much hacking of an airliner is really possible and how much is myth?
The tv show was Madame Secretary, and the premise was that she was made acting President after the Presidents plane lost all communication while over the Pacific enroute to Asia or somewhere. Yes, I know its improbable but still an entertaining show well acted and filmed. The catch is that after the Boeing lands safely the investigation finds some very sophisticated virus put into its systems by an assumed foreign power, and not just the com disable but it is claimed the virus had control of ALL the planes systems even flight and power controls. Does an airliner fly totally by wire and computer or does it have overrides to offset any glitch? Yes, I know its far fetched, its a tv drama. But hacking is real not just a myth. I have a friend who had 3 financial accouts hacked for thousands of $, which she got back, but experts could find no trace of the virus nor who had done it.

The same computer that controls the aircraft systems hosts the passenger WiFi and entertainment systems. A while back, I read about a claim that someone had hacked into the flight-control side via the passenger system.

In the classified world, this sort of thing is handled with an "air gap"... a completely independent system, not connecting to public systems in either hardware or software. Even then, all you have to do is suborn one person with the right accesses to get your nasty stuff onto the protected system.

Ron "The more they overthink the plumbing..." Wanttaja