Three weeks after cyber attacks against South Korean government websites, Seoul says that North Korea was the likely perpetrator.
Government officials investigated the attacks, which targeted websites of the presidential office and coincided with the anniversary of the start of the 1950-to-53 Korean War.
The head of Information Technology said he believed Pyongyang was behind the attacks after analysing internet addresses as well as North Korea's previous hacking patterns.
North Korea has also been blamed for an attack in March but it has repeatedly denied responsibility, saying it has also been the victim of hacking.
South Korea's defence minister told a recent conference that the North has 3,000 highly trained cyber warfare personnel.