there's an interesting question what exactly north korea's bomb was. it was roughly in the one kiloton range, usually nuclear tests are 10 to 60 kilotons. apparently it is possible to make a one kiloton explosion with conventional explosives, though in a couple of days sensors in south korea and japan should be able to rule that out if they detect radiation (low kiloton bombs leak more radiation because the blast isn't powerful enough to create a tight underground seal to keep the radioactive gas trapped)
so yeah, i'm trying to learn about nuclear weapons now. it's interesting stuff--in a horrific sort of way. but what it all means, i don't really know. the new york times quotes people who say the north korea test might be a a "partial success" or a "partial failure." i'm not completely sure what that means, actually, except that it would not be a faked test. jeffrey from arms control wonk looked at the data and called it a dud. at least one person (and i can't remember where i read it) speculated whether NoKo tested a suitcase bomb, but that seems more like an alarmist after-the-fact theory to me. but hey, what do i know? i'm just picking this stuff up
in any case, the world community seems to be operating under the assumption that the test showed north korea really is nuclear. even if it was a dud, the fact that they decided to test means that north korea at least believes that it has nuclear weapons. even if their weapons have a high failure rate, the possibility that one may work is horrible enough.
