CATIA is CAD/CAM software that Boeing uses for design/machining/testing. CATIA is made by Dassault - the French aircraft maker - and marketed by IBM here in the US.
Years ago - when I was in the business of cutting parts for Boeing - the maintenance agreement for one seat of CATIA per year was $42K. That was Boeing's cost. And they had thousands of them. Talk about subsidizing your rivals. How hard would it be for the Frogs to put invisible spyware into that code, to know what Boeing is doing? Not hard at all.
You're correct, it wouldn't be that difficult, espeically if you don't have the source available to check for the existence of such. However, with billlions of dollars at stake, any CIO worth his salt would make sure that sensetive systems are isolated, and a two way firewall is in place. Data only goes where you want it to go, when you want it to go.