Government, media and other websites in both North and South Korea were shut down today for several hours on the 63rd anniversary of the outbreak of the Korean War.
Seoul announced publicly that its websites had been hacked, raised its cyber-alert status and recommended that users improve their Internet security, the BBC reported. Pyongyang did not make any immediate comment on the shutdown of some of its websites.
South Korean websites affected by a seemingly coordinated attack included the presidential Blue House and the Prime Minister's office, along with the Government Policy Co-ordination site and some media servers.
"The government can confirm a cyber attack by unidentified hackers that shut down several sites including the Blue House," the South Korean Science Ministry stated.
North Korean sites that went offline on Tuesday morning are also likely to have been hacked, according to South Korea's Yonhap news agency.
These included the websites of Air Koryo, newspaper Rodong Sinmun, Naenara (the country's official web portal), and the Korean Central News Agency.
Hacked messages on the South Korean websites praised North Korean leader Kim Jong-un. They also credited Anonymous as the source of the hacking. The 'hacktivist' group subsequently denied any involvement with the South Korean sites via its Twitter account, but said it had succeeded in hacking a number of North Korean media websites.
Anonymous had previously announced Operation Free Korea in April which it followed up by hacking email, intranet and web servers and social networking profiles in North Korea.
The South Korean attacks were not as serious as those that occurred on 20 March. Those cyber attacks involved 48,000 machines belonging to the Shinhan, NongHyup and Jeju banks, and KBS, MBC and YTN TV stations. South Korea blamed the March cyber attacks on North Korea.
The incident followed Pyongyang's nuclear test on 12 February. Cyber attacks on South Korean websites in 2009 and 2011 have also been blamed on the North.
The Korean War lasted from 25 June 1950 – 27 July 1953 and defined the subsequent relations of the two opposed states.