South Korea has spent decades screening refugees from a hostile neighbor but some enemy agents manage to get through, underlining the challenges Western nations face in dealing with a far larger influx of people escaping the war in Syria.
Seoul uses lie detectors, interrogation and a screening process that includes keeping people in solitary confinement to catch North Korean agents among genuine asylum seekers.
Still, between 2003 and 2013, of the 49 North Korean spies apprehended in the South, 21 entered the country posing as refugees, according to the country's justice ministry.