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South Korea's national think tank on nuclear power has been exposed to a hacking attack presumably launched by North Korea, but no major data was leaked, the state spy agency said Thursday.

"An investigation is underway after receiving a damage report from the Atomic Energy Research Institute on June 1. ... It was exposed (possibly) to North Korea for about 12 days," Rep. Ha Tae-keung, a member of the parliamentary intelligence committee, told reporters, citing a briefing from the National Intelligence Service (NIS).

"It is presumed to be done by North Korea via an organization affiliated with a third country," other officials also said, adding, "No core technology data was leaked."

According to Ha and another committee member, Rep. Kim Byung-kee, the country's damage caused by hacking groups backed by national entities rose by 9 percent in the first half of the year from the second half of last year.

Ha said there were also signs showing the Korea Aerospace Industries, South Korea's sole aircraft manufacturer, may have been hacked, and currently an investigation is under way to evaluate how long it was exposed.

Referring to the physical condition of North Korean leader Kim Jong-un, the NIS said Kim is reigning the country "normally" after losing about 10 to 20 kilograms recently.

The NIS sees "there's no problem with his health," Ha said. (Yonhap)