just a thought, if north korea's nukes exploded in the atmosphere, and they said it blew up due to something (ie, mechanical failure) and they call it a success, could it be due to the fact that it was meant to blow up above the ground as an EMP? think about it.
EDIT: i agree with the people who responded, but i got the message wrong: What if the nukes that the DPRK were testing that exploded were supposed to explode above the ground to be used as an EMP test?