An opposition party lawmaker on Thursday claimed that foreign hacking groups had broken into computer systems of the state-run Agency for Defense Development and stolen military secrets.

Rep. Kim Young-ju of the main opposition New Politics Alliance for Democracy said that the hackers implanted malicious code on the agency’s main computer servers and infiltrated more than 3,000 computers.

The agency denied any hacking attempts and said that the leaked documents, some 750 pages, were not confidential and did not contain military secrets.

Kim’s claim of the leak of military secrets came amid rising security concerns due to the recent discoveries of apparent military drones, presumably from North Korea.

“Hacking groups that appeared to be Chinese and North Korean broke into the agency’s computer systems, occupied them and leaked classified military documents,” she said in a press release.

The lawmaker argued that the leaked documents were about a satellite data link system for the medium-altitude unmanned aerial vehicle South Korea is developing to strengthen its reconnaissance activities; the equipment to test the performance of the mobile surface-to-air “Singung” missile; and a software program for the guided midrange surface-to-air Cheongung missile.

Kim stressed that the documents were confidential as they carried “warning messages” that they could not be copied or cited without the permission of the publishers.

She also criticized the military authorities, saying that they still did not know when the hackers broke into the agency’s computer networks and the extent of the damage caused by the hacking incident.

Countering Kim’s claim, the ADD argued that although it controls the Internet connecting its system to external networks, its internal computer systems cannot be broken into as they are thoroughly shielded from external networks.

But the ADD said that it had requested a military investigation into the case with the possibility in mind that the email accounts of its employees with links to external networks could have been hacked into.

By Song Sang-ho (sshluck@heraldcorp.com)