It may seem like a big deal, but I'm having a hard time being super concerned about North Korea's nuclear claims.
Remember in 1998 when Pakistan announced it had successfully tested nuclear weapons and all they got was some international scolding and then got to just keep their nuclear weapons and nothing changed? Not many are seriously worried about Pakistan launching any kind of nuclear attack these days, because there's no reason. Hating India is not good enough to attack them with the kind of power that would have near every nation in the world hating them. And for North Korea, hating South Korea or the US is not enough reason either. The retaliation that would come from launching a nuclear attack would be quick and overwhelming. North Korea's regime would be out in a second. And as much as North Korea's leadership likes to put on the face of being absolutely insane in order to get what they want, I believe they're smarter than that. Having nuclear capabilities is a trophy case of wrestling awards in the living room. Impressive and intimidating, but not threatening.
The only legitimate concern I can think of is that of a country leaking a nuclear weapon to terrorists...the only people that are crazy enough to use one. But I don't really see it happening. With very few nations out there with declared nuclear capabilities, it wouldn't be too hard to figure out where it was coming from, and then that country would be squashed into oblivion.
There's even some truth to the idea that nuclear proliferation makes the world a safer place. It's the Cold War syndrome: try to match the other so that neither will attack. If nations have the ability to turn major cities into parking lots with one bomb, they are not going to use them if they know that the country they're attacking will come back with the same force. So everyone sticks to "civil" conventional weapons.
It's too bad that we have to put sanctions on North Korea over this. They should have some sort of punishment, and military involvement is most definitely not worth it and just saying "bad North Korea" does nothing, so economic sanctions is really all we can do. But I hate that the country is gettting even less money in while its people are starving. The people are starving while the regime puts their funds towards weapons programs. That's the real crime. Not having the weapons, but putting money that could be going to so many better things on weapons.
Something I've never understood: why in the world don't more nations have nuclear capabilities? The US had them for 50 years, and we can't possibly be that technologically ahead of other nations. I understand that there are many nations out there that don't want nuclear weapons, but how are there still people that are trying to do it and can't?