People who don't understand computers imagine that hackers can do the impossible. When someone takes control of another computer through a network, they aren't really applying control remotely, they are simply taking advantage of that computer's willingness to volunteer that control.
These holes in security are provided intentionally by the makers of the computer systems being attacked. Microsoft wants it to be easy to modify software, within PCs, from a remote location.
An aircraft's flight control network has a completely different architecture, than a Windows network. It is safe to assume that the two are connected through a proprietary device that converts data between the two networks, but cannot create control signals on the flight control network.
Boeing can make it so that it is no easier for a hacker to gain control of the flight control systems from a passenger seat, than it is to gain control of the power lines through my ADSL CODEC.
you are not incorrect and perhaps I am giving hackers more credit than is due. that being said, I would still feel better if these networks were completely and totally separate. IMHO, joining them in any way, form or function isn’t sound.