I wasn't saying it was only secure due to obscurity. I should asked more clearly - "So the idea is to enhance security through obscurity?" For mission critical

I wasn't saying it was only secure due to obscurity. I should asked more clearly - "So the idea is to enhance security through obscurity?" For mission critical secure systems, I can see a case being made that software should be closed source, as it allows fewer people to be aware of potential attack vectors. Especially, if you know the software you are creating won't be used externally much or audited.