We don't know to this day whether NoKorea has successfully detonated a Plutonium bomb. We know they are refining and stockpiling the metal, but a number of blasts observed in North Korea going back several years have all been estimated at sub-kiloton range [they've been detected via listening devices because they haven't even been powerful enough to tweak the seismometers -- at least not the civilian ones.]
Some weapons experts speculated at the time that those tests weren't even "kind of successful" low-yield. It's actually possible that they got themselves blown up improperly handling the high explosives needed for the implosion, and the results seen weren't nuclear explosions at all.
I blame Tom Clancy. He made it seem like dumb ass terrorists might pull it off, which must mean it’s easy. People forget his dumb ass terrorists started with a mostly working bomb, and then it didn’t detonate properly. Really folks, if it was that easy there’d be no point in the non-proliferation agreement and these negotiations because everybody would already have the bomb.