The Korean Communications Commission told Yonhap it detected distributed denial-of-service attacks beginning at 10:45 a.m., but the sites of the presidential office, the Ministry of Foreign Affairs and Trade, the National Assembly and banks were all operating normally.
The agency said antivirus software was effective, and "zombie computers" that can be hijacked to carry out such attacks were turned off in time.
Attacks on the Web sites of the presidential office and Defense Ministry were detected Thursday, followed by wider disruptions Friday.
"While the attacks on Friday caused some disruptions, the severity has diminished," the commission said.
Korean antivirus developer AhnLab said it is screening for mutations of the latest attack but expects any damage to be limited.