I doubt that Sony has ruled out the possibility of it being an inside job, or done with the help of someone who has knowledge of their network and systems, but

I doubt that Sony has ruled out the possibility of it being an inside job, or done with the help of someone who has knowledge of their network and systems, but it's still very possible this was the work of outsiders. Unfortunately we'll probably be left guessing as to how this hack happened and how long it went on, since Sony is not likely to ever release that information even if they figure out the cause.