Could I just add that I think it's important to understand that if a weapon from any of these countries wound up in the hands of a terrorist, it would involve the most extraordinary retribution against that country. It would be a huge gamble. Even Afghanistan's harbouring of Osama bin Laden—it didn't involve nuclear weapons, but just harbouring him—involved massive military intervention there. It would be a huge gamble for a state to think it could provide that kind of weaponry to a terrorist group and not have it detected.
It's more a question of the theft, the accidental use, or the kind of activity that, for example, happened with A.Q. Khan in Pakistan that is really very worrisome.