But the agency says it only intended to strengthen its monitoring of rival North Korean agents, not South Koreans.

The office of lawmaker Shin Kyung-min said National Intelligence Service chief Lee Byoung Ho told legislators in a closed-door briefing that the agency bought hacking programmes from an Italian company in 2012.

Lee didn't indicate whether that included technology for hacking Kakao.

The NIS has a history of illegally tapping South Koreans' phone conversations.

Seoul blames Pyongyang for repeatedly attacking Internet networks and stealing information from computers. The spy service didn't immediately return calls seeking comment.