South Korea believes North Korea was behind cyber attacks against several websites last month, officials say.
The attacks, which took place on the anniversary of the Korean War, hit the presidential office website, and several other official and media sites.
Investigators said an IP address used in the attack matched one used in previous hacking attempts by Pyongyang.
The North has also been blamed for cyber attacks on six South Korean banks and broadcasters in March.
"We speculate the hacking was done by North Korea," Park Jae-moon, a director-general at the Ministry of Science, ICT and Future Planning, said.
Analysis of "82 malignant codes [collected from the damaged devices] and internet addresses used for the attack, as well as the North Korea's previous hacking patterns," showed that "the hacking methods were the same" as those used in the 20 March cyber attacks, he added.
"[A] North Korean IP [address] was found in passages of the malignant codes and some of the damaged organisations. I can say this is the decisive evidence," Mr Park said.
Almost all the websites and servers affected by the attack had been repaired, he added.
The hackers attempted to steal personal information from the websites, AP news agency reported, citing investigators.
"The cyber attack seriously undermined the country's image by [altering] the websites of symbolic government organisations, such as the presidential office Cheong Wa Dae," the science ministry said in a statement.
Those behind the attack also "caused confusion... by assuming the identity of the hacktivist group Anonymous", the ministry added.
During the 25 June attacks, messages praising North Korean leader Kim Jong-un and claiming that hacking collective Anonymous was responsible were left on the hacked websites.
North Korea has not commented on the hacking accusations.
In the past, it has accused both the South and the US of preventing users from being able to visit its official media sites.
On 20 March, cyber attacks on banks and broadcasters in the South affected 32,000 computers and disrupted banking services.
South Korea blamed that incident - which came at a time of heightened tensions between the two Koreas following Pyongyang's nuclear test on 12 February - on North Korea.
North Korea has also been blamed for previous cyber attacks in 2009 and 2011.