Suspected cyber attacks paralyzed Web sites of major South Korean government agencies and banks and other Internet sites. Officials say these attacks are linked to similar attacks that occurred here in the U.S.
A spokeswoman at Korea Information Security Agency said that many government agency Web sites are down or had problems since late Tuesday.
Eleven organizations were affected, including the presidential Blue House, the Defense Ministry, the National Assembly, Shinhan Bank, Korea Exchange Bank and top Internet portal Naver.
South Korea's main spy agency, The National Intelligence Service, said the attack was prepared by pro-North forces. The agency was cooperating with the American investigative authorities to examine the case. An estimated 12,000 computers were infected locally and 8,000 abroad, they said.
But there have been no immediate reports of financial damage or leaking of confidential information.
The U.S. sites were hit by a widespread computer attack that began over the holiday weekend.
The Treasury Department, Secret Service, Federal Trade Commission and Transportation Department Web sites were all down at varying points, U.S. officials say. The sites continue to have difficulties signaling a more sophisticated attack than expected.