Kim Jong Un wants the attention of world powers and wants to be a world power. Because he doesn't have the military might to make a dent worth spitting at, he's established an irritating cyber-space program, one that can take down a Sony movie.
Obviously, the world powers will find a way to counter the attack. Then hackers all over the world will find a loophole and attack again. Back and forth, back and forth, until the whole system is brought down in chaos and we revert to living in caves.
Might even have to write letters again.