SEOUL, SOUTH KOREA - South Korea's presidential mansion, the Blue House, has come under cyber-attack from overseas hackers who accessed some confidential information, officials said Tuesday.

The attacks were discovered about two weeks after they happened when the entire computer network underwent a security check in early March, the Blue House said in a statement.

"Some files infected with Worm virus have been found," it said.

The statement blamed the absent-mindedness of an unidentified official who worked at the National Security Council of former president Roh Moo-Hyun.

"The official's private files and some other information was leaked," it said.

Hackers again mounted attacks on the Blue House on Saturday but they were unable to break through firewalls or other security programmes, it said.

"Punishment procedures against the official are underway," the statement said, adding measures to strengthen cyber-security have been completed.

The Hankook daily reported that the hackers, who it said were believed to have been operating from China or North Korea, installed "backdoor" programmes to bypass normal access procedures.

The incident raised fears they might be trying to collect sensitive security information, the daily said.

It said the Blue House on-line system failed to work when the new president Lee Myung-Bak took office on February 25, and it took 10 days before it was back to normal.

South Korea's Internet industry has already been rocked by the news that the personal information of 11 million users of Auction, the country's largest e-marketplace, was leaked in a hacking incident.

South Korea is one of the world's Internet powerhouses but its on-line security is considered lax.

Increasing numbers of hackers are targeting South Korean Internet sites from China or going through poorly protected China from third countries. --AFP