It would have been more convenient for the USG to blame ISIS but nobody would believe that.
I still don't buy the N.Korea angle. They would just love the propaganda. They are quite happy to provoke the US with missile tests publicly, you don't think a hack like this they are going to want to keep quiet?
Doesn't make sense to me.
The Interview was never mentioned by the hackers until after the media starting running with the story
North Korea threatened war over this movie - http://www.bbc.com/news/world-asia-28014069
Now again, North Korea's words are kind of cheap, but they were talking about as big as you can get before this hack, and then specifically warned Sony to "obey" them. We have absolutely no idea what communications happened between the group and Sony and then law enforcement, so the whole what the media reported angle seems rather spurious. Sony/Law Enforcement, people who know more than us, seem to believe it was related to the movie.
Actually, there is. They tend to huff and puff about American military exercises that occur in cooperation with the Japanese or the South Koreans, or to complain to the UN about various things (e.g.: the CIA torturing people). But their MO, such as it is, is to complain and threaten, almost exclusively. Occasionally they will perform a missile test that causes concern, but those missiles land in the Sea of Japan or some other body of water, not anywhere that causes actual harm.
No, this goes against the DPRK's MO up until now. If they are responsible then it is a shift in their tactics from "loud and threatening, but basically harmless to other nations", to "actively and publicly committing acts of economic espionage." That would be quite a departure for them.
North Korea is suspected in a number of similar attacks. Because really, what is anyone going to do? Attack them? They have nukes. Isolate them? They can't possible be more isolated. Sanction them?
As an aside, the regular threat of using nuclear weapons is an act of extreme violence, and I doubt North Korea's neighbors treat it so flippantly. The threat is unlikely, but extremely real.