Police are investigating a large-scale cyber attack on the JoongAng Ilbo that crippled its servers and website on Saturday.

Some raised suspicions of North Korean involvement as the incident followed its threat to attack major media companies in the South.

According to the Seoul Metropolitan Police Agency, the incident took place from around 6:30 p.m. on Saturday when one of the two main domains of the newspaper, www.joongang.co.kr, shut down. When accessed, a picture of a white cat grinning and covering its mouth took up the page. Beneath the picture were the words, “Hacked by IsOne,” and complicated codes marked in green. Experts said the codes indicated possible additional hacking of other media companies.

Right after the attack was detected, JoongAng directed users to another domain, joongang.joinsmsn.com, so that users could still access content.

However, the newspaper reported that the hackers cracked into the main server of the company’s cyber system and that the production of the newspaper’s Monday edition suffered from the malfunction. An insider said all workers were on emergency duty on Sunday and substantial data may have been destroyed for good.

There have been cases in other countries of media websites being hacked by those wanting to boast or present their message. But hacking into the main server to shutdown down the whole system is unprecedented, according to online security experts.

Investigators said they have started tracing the routes of the invader with the cooperation from the Korean Internet Security Agency.

They are not ruling out the possibility that North Korean hackers are the major culprit as the communist state earlier this month threatened to attack media companies.

On June 4, the North Korean People’s Army announced that its soldiers are “asking for attack orders on President Lee Myung-bak and South Korean media companies that have dishonored its regime.” It suggested a pile of coordinates, marking MBC, KBS, SBS and CBS broadcasting stations as well as Chosun and JoongAng newspaper headquarters as targets.

“We are looking into every possibility,” said Jeong Seok-hwa, head of the police Cyber Terror Response Center.

By Bae Ji-sook (baejisook@heraldcorp.com)