If DPRK has the capacity to pull this sort of hacking feat on demand, it begs the question: why aren't they doing it around the clock, to hurt their enemies that they seem to hate so much? It's just not very realistic to think that DPRK has this super secret hacker army (but not so secret that we haven't heard of it in the media) that can hack any large corporation (but can't cover its own tracks). If they did, we would see it action all year long.

This hack sounds like the work of a large, professional, well-funded organization that only uses its capabilities in a very targeted, parsimonious manner. But what would be the motive for the US govt to hack Sony and then accuse DPRK? Distract the public from the CIA torture report? Something else?