Since last March 26th, when a North Korean sub torpedoed and sank a South Korean warship, the South Korean military, and many civilians, have been especially alert to more North Korean military mischief. So the alarm was given on the night of June 16th, when civilians in Ansan, 35 kilometers southwest of the South Korean capital, reported seeing parachute-like objects drifting down into a nearby mountain. This set off alarms, because North Korea has airdropped terrorists and spies by aircraft before (a long time ago) and have trained thousands of commandos to do it in a future war.
The army and police put together an armed force and went up into the hills after daybreak. Eventually they found several dozen helium balloons that had been released, it was later found out, by young schoolchildren on the 16th. There have been similar incidents. Ten days before the balloons, there was an explosion on an island near the sea border with North Korea, and investigating troops found a diving suit on a beach there. North Korea has a long history of landing terrorists and spies via submarine. But this time, the explosion and diving suit were late found to have nothing to do with North Korea. But South Koreans are still on edge, and will probably remain that way for the rest of the year.