A suspected hacker posted more illegally obtained information on two South Korean nuclear reactors Tuesday, continuing its demand for their suspension amid the growing worries over the cybersecurity of the country‘s critical facilities.

Through an unidentified Twitter account around 3 p.m. in the day, the suspect made public four zipped files that contained drawings of some reactors and the URLs of articles on reactor-related technologies, which are held by the Korea Hydro & Nuclear Power Co.

According to investigative agencies, the four files involve the designs of Gori reactor units 1 and 2 and Wolseong reactor units 3 and 4, while the URL-attached articles contain introductions to a safety analysis code.

The suspect, self-identified as the “chairman” of the antireactor entity, demanded the KHNP make an apology to the entity, hinting at further data leaks if there is no move from the government for negotiations.

In early Tuesday, President Park Geun-hye called on officials Tuesday to beef up the cybersecurity of the country’s nuclear reactors and other key infrastructure facilities following cyberattacks in South Korea and the U.S.

The call comes as South Korea is striving to find those responsible for a series of leaks of information related to two nuclear reactors. Officials said the Gori and Wolseong nuclear power plants, both located more than 400 kilometers southeast of Seoul, remain safe as their innermost networks are completely cut off from the Internet, though the latest incident raised safety concerns.

Park urged officials to “fundamentally recheck the preparations against cyberterrorism on our nation’s key facilities, including nuclear reactors,” in a Cabinet meeting in Sejong.

The suspect first publicized personal profiles of some of the 10,799 employees of the reactor operator KHNP in blog postings on Dec. 15.

The cybercriminal then on Dec. 18 and 19 posted internal information on Twitter on the nuclear reactors such as floor plans, demanding the shutdown of Gori reactor units 1 and 3 and Wolseong reactor unit 3 for three months from Dec. 25.

In the post on Sunday, the suspected hacker made public the designs and manuals of Gori reactor unit 2 and Wolseong reactor unit 1, taken from the KHNP. Among the leaked information were details on the reactors’ air conditioning and cooling systems.

By Kim Yon-se and news reports (kys@heraldcorp.com)