Pyongyang is believed to have begun sending spies posing as defectors to the South in the late 1990s when large batches of refugees fled a massive, deadly famine.
Before that, South Korea occasionally caught armed spies who had infiltrated from across the militarized border, or via small submarines in the dark of night. Some confrontations between North Korean agents and South Korean security forces ended in deadly gunfights.
“It is not an easy process because they are disguised as refugees, highly trained, dispatched by counter-South espionage agencies,” said Jun Ok-hyun, a former deputy director of South Korea’s spy agency who retired in 2009.
“The more defectors come, the stronger the review process should be because it could be easier for North Korea to send spies as fake refugees,” he told Reuters.
When defectors leave the resettlement center and move into the general population, police officers are assigned to protect and manage them, according to police officials who declined to elaborate.