[egeozcan]

Oh I see. Thanks for the detailed explanation. Just have these questions: Without that patents file and the rights granted within, could Facebook theoretically sue you for infringing their patents by using their own open-source software? If not, what's the raison d'être for such a grant?

[mbrock]

This is the question of whether free software licenses without patent granting clauses have an "implicit patent license", and from what I can tell it's not clear cut.

http://en.swpat.org/wiki/Implicit_patent_licence

It seems likely that judges would agree that free software licenses come with some sort of implied patent license, but it's unclear how that interacts with modification and redistribution, etc.

[carussell]

> 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.