South Korea's state-run nuclear power plant operator said it started a two-day drill on Monday to prepare for a potential cyberattack, after a series of online document leaks caused increasing security concerns.
The stolen documents include blueprints of climate control systems, floor plans, software program manuals and personal information of employees. The leaked documents, however, do not have classified information and pose no threat to the safety of the nuclear plants, said Korea Hydro and Nuclear Power Co.
The leaks, posted online by the self-proclaimed "anti-nuclear reactor group," included a statement that 100,000 more pages of documents will be posted and a "second round of destruction" will be launched if the government fails to close down three nuclear plants by Christmas.
The power plant operator has not confirmed whether the data leak was hacked by an outsider or stolen by an insider. The operator said it first detected malicious code in email on Dec. 9. The stolen documents were posted on a blog and via Twitter at different times last week.
The South Korean operator runs 23 nuclear plants, supplying about 30 percent of the country's electricity.
The police and prosecutors are investigating whether the leak is related to the recent hack of Sony Pictures. The U.S. Federal Bureau of Investigation Friday said North Korea was responsible for the attack. The North Korean government, however, has denied the allegations.