The South Korean military said Saturday it is investigating a case that local news media said entailed a leak of highly sensitive information regarding Seoul's intelligence agents spying on North Korea.
The Korea Defense Intelligence Command, a secretive branch of the South Korean military, discovered about a month ago that classified information, including personal data of its agents stationed overseas, had been leaked, according to Seoul's Yonhap News Agency.
Officials have since "detected signs" that the leaked data may have reached the nuclear-armed North, the Yonhap report said.
The case is "currently under investigation by military authorities," the defence ministry said in a statement, without confirming the local reports.
The military plans to handle the case "sternly in accordance with laws and regulations according to the results of the investigation," it added.
The announcement came days after the United States, Britain and South Korea issued a joint warning on Thursday that North Korean hackers have conducted a global cyber "espionage campaign" to steal classified military secrets in an effort to advance its banned nuclear weapons programme.
The leaked information reportedly included information about South Korean agents posing as diplomats overseas, as well as undercover agents, with some of them even returning home due to concerns about their identities being revealed, according to Yonhap.
Authorities are investigating a civilian official at the military intelligence command after discovering that the organisation's classified information was stored on the official's personal laptop, Yonhap said.
The official is suspected of leaking the information via the laptop, but has reportedly claimed that the device was hacked, South Korean media reported.
Yonhap said authorities are investigating the possibility that the official intentionally left the laptop vulnerable to hacking by North Koreans.
North Korean hackers "currently target sensitive military information and intellectual property of defense, aerospace, nuclear, engineering organisations," the Thursday joint warning by Washington, Seoul and London said.
In May, Seoul police said North Korean hackers stole sensitive data, including South Koreans' individual financial records, from a South Korean court computer network over two years.
Meanwhile, Seoul's spy agency said in February that North Korean spies were using LinkedIn to pose as recruiters and entice South Koreans working at defence companies so the spies could access information on the firms' technology.
