A new analysis suggests North Korea clandestinely tested two nuclear weapons in 2010. If it's true, it would double the number of known tests hailing from the country and could mean serious nuclear warhead development is underway.
Remember when North Korea made that bizarre claim in May 2010 that they had achieved nuclear fusion? This might explain why. Western media mocked the announcement, but a small circle of experts who do nothing but hunt for covert nuclear tests were worried for real. Nature reports that "South Korean scientists had detected a whiff of radioactive xenon at around that time, hinting at nuclear activity in its northern neighbour."