The Freetrack code is public. It's published
here. If NaturalPoint had any copyright claims against the code, they were dealt with several releases ago. They have access to read the code as often as anyone else. There is not a lot of code and NaturalPoint have made requests for lines to be removed before, which were complied with. So it would appear that there's no longer any code that's original to TrackIR in there anyway. And in any case, infringing copyright would be essentially impossible given that the TrackIR programs and drivers are supplied as binaries. To say that they've "hacked" the interface is just to say that they've worked out how to provide the correct input to the game. There's certainly nothing illegal about that. Sani's FOV Changer is more of a hack than that, it changes data in memory to change the FOV in Il-2.