Seoul, March 17 (IANS): North Korea is believed to be linked to a series of recent data leaks from South Korean nuclear power plants, investigators said on Tuesday.

In December 2014, an unidentified hacker posted blueprints of nuclear power plants and threatened to destroy the facilities while demanding they be shut down.

Last week, the hacker -- while demanding money -- posted more files on Twitter that included documents concerning the country's indigenous advanced power reactor.

Announcing the interim results of its probe into the high-profile case, a special investigation team said the series of incidents "is believed to have been caused by an (unidentified) group of North Korean hackers who aimed at causing social unrest and agitating the people", Yonhap News Agency reported.

Pointing out that the compromised data "are far from critical", the investigators said the hackers stole it by hacking e-mails and online communities of former and current officials of the Korea Hydro and Nuclear Power Co. (KHNP) instead of directly infiltrating the operator's network.

"We've learned that the malicious code used in the e-mail attack in December was similar to what North Korean hackers usually employ," an official of the investigation team said.

"Multiple internet protocol addresses used for the attacks were found to be based in North Korea," he said, explaining the reasons for its conclusion.