Prosecutors said Friday that they have found no evidence to incriminate any Grand National Party lawmaker in connection with the Oct. 26 cyber attack on the website of the state election watchdog.

They concluded that the attack was plotted and carried out by a former secretary of the National Assembly Speaker Park Hee-tae and another ex-aide of former GNP lawmaker Choi Gu-sik. They hacked the website of the National Election Commission with a distributed-denial-of-service attack from 5:53 a.m. for three hours.

The scandal has shocked the nation as well as political circles. Opposition parties have stepped up their offensive against the GNP, raising suspicions that the ruling party may have masterminded the attack in a bid to prevent the opposition-backed independent candidate Park Won-soon from winning the high-profile Seoul mayoral by-election.

The two lawmakers’ former aides planned the attack in an apparent attempt to lower the turnout of young voters who supported the opposition candidate, investigators said.

Park’s former aide surnamed Kim gave 10 million won ($8,600) to an IT firm head surnamed Kang, through Choi’s former secretary Kong, for the attack, the prosecution said.

“They plotted the attack under the belief that the paralysis of the NEC website could lower the voter turnout by blocking voters, especially young voters, from finding the locations of polling stations on the website, and in doing so discouraging them to give up voting to make the situation favorable for their party’s candidate,” a prosecution official said.

A DDoS attack, which swamps selected websites with massive traffic, uses virus-infected “zombie computers” to simultaneously access them. All of those used for the attack have been seized as evidence.

Election analysts had said that Park could gain more votes when many young progressive voters turned out in the high-stakes Seoul mayoral by-election pitting him against GNP candidate Na Kyoung-won.

By Song Sang-ho (sshluck@heraldcorp.com)