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.
