> could Facebook theoretically sue you for infringing their patents by using their own open-source software Yes, but only because the question "can X sue you f

> could Facebook theoretically sue you for infringing their patents by using their own open-source software Yes, but only because the question "can X sue you for Y" is true for any X and Y. Licenses can't protect you from being sued; the only thing they can offer protection from is someone else winning a suit against you.