Security alert: A man walks by a gate at the Cyber Terror Response Centre of the National Police Agency in Seoul. Photo: AP
Seoul: Official South and North Korean websites have suffered what appears to be co-ordinated attacks by unknown hackers on the anniversary of the outbreak of the Korean War, prompting Seoul to issue a general cyber alert.
The affected websites included those belonging to the South's presidential Blue House and a number of the North's state-run media groups.
South Korea raised its five-stage national cyber alert on Tuesday from level one to two in the morning, and then again to three after the scope of the attack became clear.
Park Jae-moon, director of the Science Ministry's IT Strategy Bureau, said the websites of 11 media outlets, four government agencies and a political party had been shut down.
"It's like an endless fight between spears and shields," Mr Park said, adding that it was too early to say who was responsible.
Some sites were operating normally again in a matter of hours, while some remained offline well into the evening.
The hacking coincided with the 63rd anniversary of the start of the Korean War on June 25, 1950.
Investigations into past large-scale cyber assaults on South Korean media groups and financial institutions have concluded that they originated in North Korea.
A number of posts left on the hacked South Korean sites claimed to be the work of the global "hacktivist" group Anonymous and included messages praising North Korean leader Kim Jong-Un.
Anonymous denied any involvement on its official Twitter account, but said it had succeeded in hacking a number of North Korean media websites on Tuesday, including the official Korean Central News Agency (KCNA) and the ruling party newspaper, Rodong Sinmun.
Both sites were briefly inaccessible on Tuesday morning but appeared to be running normally a few hours later.
There was no immediate statement from the North, either confirming or commenting on the attack.
South Korea has sought to beef up its cyber defences since a March 20 attack completely shut down the networks of TV broadcasters KBS, MBC and YTN, halted financial services and crippled operations at three banks.
An official investigation determined North Korea's military intelligence agency was responsible, with a joint team of civilian and government experts tracing the origin to six personal computers used in North Korea.
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