How North Korea, a nation with what is one of the worlds most primitive computing/ internet facilities, has the ability to carry out what appears to be a sophisticated attack that walks away with almost every drop of data Sony has in its possession. Even a couple of random sympathisers should not have been able to do the job.
Sony has not got many friends in the world, mainly due to restrictive copyright practices and DRM. It would surprise me less if some groups who were opposed to this had over a long period of time, wormed their way into Sonys network, and after being confident they could see everything, struck at an opportune moment.
Or it could be Adam Sandler, highly pissed at the lukewarm enthusiasm with which Sony release another of his movies...