Yes of course. The old argument that Linux is free of backdoors because it is open source. It's such a ridiculous claim. Software systems on that scale are so complex, there is NO way whatsoever to make sure there isn't a backdoor in there. I would go as far as saying that OpenSource software by definition is more vulnerable to backdoors than closed source software, exactly because the source code is available and anyone with some credibility can make patches. It is the dreamland scape of the NSA.

Hacking into closed source code is much more dangerous (politically) for them and also more difficult.