South Korea's nuclear research institute has been exposed to a cyber attack, likely perpetrated by North Korea, for 12 days. 

The National Intelligence Service(NIS) revealed the hacking incident at a parliamentary committee hearing on Thursday. The spy agency told lawmakers that it believes a group linked to North Korea was behind the attack, according to ruling Democratic Party lawmaker Kim Byeong-ki and main opposition People Power Party(PPP) lawmaker Ha Tae-keung.

The two lawmakers, who serve as members of the intelligence committee, said the NIS does not believe the culprits were able to access material on key technology. 

The NIS told committee members damages from state-sponsored cyber terrorist organizations rose nine percent in the first half of this year from the previous six months.

Rep. Ha, a senior member on the intelligence committee for the PPP, said the Korea Atomic Energy Research Institute(KAERI) reported the data breach on June 1. Ha added that the agency was likely targeted for 12 days.

Ha said a separate investigation is underway after the Korea Aerospace Industries(KAI) was also allegedly a target in a cyber attack.

Regarding North Korean leader Kim Jong-un, who recently appeared notably slimmer in official photographs, South Korea's top spy agency said it seems Kim has lost between ten and 20 kilograms and is overseeing state affairs as usual.