The prosecutors’ office has recently arrested five core members of a North Korean espionage network that has allegedly been operating for more than a decade in South Korea. It has also indicted another five without detention, charging them with espionage.

What should come as a surprise is not that North Korea has been operating such a large spy ring but that it has avoided discovery for such a long period of time. What have the South Korean counterintelligence agencies been doing all this while? It is the first time in a decade that North Korean espionage activities of such a scale have been exposed.

The espionage activities go back to 1993 when a South Korean activist made a secret visit to Pyongyang. At the time, the man was allegedly told by the late North Korean leader Kim Il-sung to establish a regional organization for a “revolution in South Korea.” The prosecutors’ office says he was a pro-North Korean activist when he was a university student.

When a spy network was put in place in 2001, the office says, the ring leader began his espionage activities in earnest, posing as a businessman after setting up an information technology company. Another suspect was an aide to a National Assembly speaker.

The office says these findings were from the materials it had obtained in the offices and homes of the suspects, adding that they were not responding to its inquiries, exercising their right to silence. It also says that they were ordered to help unify split progressive forces, gather information on military installations and infiltrate political organizations.

As the criminal investigation extended to members of progressive forces, the Democratic Labor Party and others accused President Lee Myung-bak’s administration of engaging in McCarthyism. But they were mistaken in making such a response, given that some of their members have been convicted of espionage in the past.

What the progressive political parties and labor organizations need to do is make no attempt to put any obstacle to the ongoing investigation. Instead, they should voluntarily cooperate with the prosecutors’ office, which is conducting an investigation into a matter of national security.

The National Intelligence Service and other counterintelligence agencies will have to enhance their vigilance against North Korea’s espionage activities. This spy ring may be the tip of the iceberg.