North Korea is believed to have again released leaked data on South Korea's nuclear power plants on the Internet, Seoul investigators said Thursday.

The confidential data of South Korea's nuclear power operator the Korea Hydro and Nuclear Power Co. and blueprints of several plants were posted on the U.S. Website on Wednesday, according to a special investigation team probing the case.

In December, an unidentified hacker, claiming to be an activist against nuclear power, had posted data about local nuclear power plants, including their blueprints, five times and threatened to destroy the facilities while demanding they be shut down.

Again in March, the hacker renewed its threats by posting more files on Twitter that included documents concerning the country's indigenous advanced power reactor 1400, while demanding money in exchange for not handing over sensitive information to third countries.

"We are taking note of the fact that the suspect renewed activities just in time for the 21st anniversary of the death of Kim Il-sung," said an investigator, adding that the team is looking

into whether release was done in the same way as the two previous ones.

The team previously released its investigation outcome that the leakage is "believed to have been caused by an (unidentified) group of North Korean hackers." (Yonhap)