I might be naive but I still don't see a smoking gun. I realize in these situations it is hard to dig up unassailable evidence one way or the other. The author seems to be making the assumption that the only party that would be interested in intelligence on joint US-South Korea military exercises would be North Korea. I would imagine that China, Russia and Japan might be interested as well. Disrupting South Korean banks could just as easily be the work of Chinese or South Korean hackers, right? I see a correlation, but not necessarily a causation.