Spying missions still de rigueur for isolated North
Khang Hyun-sung in Seoul
Alleged agent arrested last month has crossed into South three times
Inter-Korean ties may have progressed since the darkest days of their cold war, but one thing has not changed - the north's penchant for spying on its neighbour.
The point has been proven with the arrest of alleged North Korean spy Chung Kyung-hak, 48, who was detained late last month after being caught trying to enter the South on a forged Philippine passport.
South Korea's national intelligence agency said this week Chung had entered the country at least three times in the past decade.
'The presumption has to be that North Korean infiltration of the South was, and perhaps still is, routine,' said Aidan Foster-Carter, a commentator on Korean affairs.
Part of the reason the recent arrest has garnered headlines is that this is the first such arrest under the administration of President Roh Moo-hyun, who has been pursuing a policy of engagement with the North.
'Countries have intelligence services and even when relations get better they will do their best to get information and given that North Korea has used infiltration in the past, I see no reason to assume they would have stopped,' Mr Foster-Carter added.
The most daring spy mission from the North came in 1968, when Pyongyang sent a commando unit to assassinate then South Korean president Park Chung-hee.
The spies managed to get within sight of the presidential Blue House before being killed in a gun battle.
In 1998 a North Korean submarine was caught in South Korean fishing boats' nets.
When the vessel was towed ashore, the nine crew members were found shot dead in an apparent group suicide.
Baek Seung-joo, of the Korean Institute for Defence Analysis in Seoul, said that through his contacts he had seen a copy of North Korea's war plan for the South and discovered the crucial role of spies.
'[North Korean leader] Kim Jong-il argued they could attack South Korea's non-military facilities such as its nuclear power plants and much of the [North's] information and photos of the South's nuclear facilities had been collected by spies,' Dr Baek said.
'They have been essential for developing an attack plan for South Korea.'
But the flow of spies has not only been one way. In recent years former South Korean spies have shed light on the existence of a secret special operations agency, the Headquarters Intelligence Detachment, set up more than 50 years ago by Seoul to send spies into the communist North.
'We estimate that over the space of half a century, there were about 9,000 people sent to the North, of whom 8,000 died. Our primary aim is to get a full accounting of their fate and to let South Koreans know of their work,' said Ha Tae-joon, the chairman of the Korean Association for the Survivors of Special Operations, one of the pressure groups former spies have formed for recognition and compensation.
Contrary to stereotypes, most of the recruits were not military men but ordinary civilians lured by the promise of rich rewards in return for infiltrating the North. But for most, the rewards never came.
Analysts suggest that since the 1970s, the use of more sophisticated satellite intelligence systems by South Korea and the US made the use of spies redundant.