The South Korean parliament on Thursday approved a bill allowing a special investigation into an election-day hacking of the national election watchdog's website.

The bill, passed in a 183-9 vote in the 299-member parliament, will now require President Lee Myung-bak to appoint a prosecutor to reinvestigate the cyber attack on the National Election Commission's website on the day of October by-elections.

The investigation will also look into a similar attack on the website of Seoul mayor Park Won-soon, then an independent candidate backed by the liberal camp.

After a separate probe, prosecutors said earlier this month an aide to a ruling party lawmaker and a secretary for former ruling party leader Park Hee-tae orchestrated the distributed denial-of- service (DDoS) attack that shut down the websites for two hours on Oct. 26.

The two aides were arrested last year, along with IT administrators who were also involved in the attack.

Despite the findings, the opposition camp has alleged high- ranking officials of the conservative ruling Saenuri Party, formerly the Grand National Party, might have ordered the attack to prevent younger, liberal voters from locating polling stations.