S. Korea Raises Security after Cyberattack on Nuclear Plants

South Korea has increased security at its nuclear power centers. South Korea took action after computer hackers entered the power centers' computer networks and released sensitive documents on the Internet.

South Korean officials are trying to show the public that the country's 23 nuclear reactors remain secure. They want to show that recent attacks on the Korea Hydro and Nuclear Corporation cannot affect the computer systems.

The hackers used e-mail addresses of retired employees to put 300 kinds of bad software called "malware" in the company's computer network. They have already released drawings of the plants' systems as well as information about tests of the centers. They also have released information about how much the centers' workers are paid. They are threatening to damage three nuclear plants unless the government closes them.

The unidentified hackers said they oppose nuclear power. Simon Choi is a top official of a company that helps protect against computer attacks. He says this attack does not appear to have come from an anti-nuclear group.

Mr. Choi says what these attackers are doing is very similar to what North Korean hackers did in earlier attacks. He says they are using Twitter or another site, called Pastebin, to publish secret documents. He says accused North Korean hackers did the same thing last year when they attacked computers in the office of the South Korean president and in the Sony attack.

American officials have accused North Korea of illegally entering the computer system of Sony Pictures Entertainment in the United States. The hackers were trying to stop the release of a comedy movie about the imaginary killing of North Korean leader Kim Jong Un. South Korean officials have also said North Korea is responsible for recent attacks on the computers of South Korean government agencies, television broadcasters and media websites.

Officials have increased security around the targeted reactors. Heavily armed troops surround the areas. The defense ministry's cyber warfare unit also is working to stop any further attacks. Mr. Choi says the systems that control the nuclear reactors are separated from other computer networks, so it is not possible for hackers to enter the control systems.

He says the network can only send information, not receive it, so it is difficult for hackers to enter.

The hackers say they are in the American state of Hawaii. However, investigators say the suspects used Internet addresses based in China, in an area where officials believe North Korean hackers work.

A South Korean justice ministry official says the South cannot confirm that North Korean hackers are to blame for the attack. However, they believe it is possible.

About one-third of electricity used in South Korea comes from nuclear reactors. It is the fifth-largest user of nuclear power in the world.

I'm Christopher Cruise.

VOA Correspondent Brian Padden and VOA News Producer Youmi Kim reported this story from Seoul. Christopher Cruise wrote it for Learning English. Mario Ritter was the editor.