I remember a discussion on HN (I think) about the Skype windows client, where an ex-dev told tales about how horrible their code base is. It sounded like an engineers nightmare. They also employ(ed?) several obfuscation techniques and stuff like runtime memory encryption, just to 'protect' their protocol from being reverse engineered. I can imagine that things didn't improve much over the last decade and that their Android/iOS app doesn't look much better internally.