That's because it is likely the hackers, whoever they are, used the addresses to disguise themselves — for instance, by accessing the computers from a remote location. IP addresses can also be faked or masked, hiding their true location.

South Korean media reported in May that North Korea was running an Internet warfare unit that tries to hack into American and South Korean military networks to gather confidential information and disrupt service. The Chosun Ilbo newspaper reported Friday that the North has between 500-1,000 hacking specialists.

The fact that some of the attacked sites — such as the ruling party and the office of President Lee Myung-bak — have links to the South Korean government's hard-line policies toward the North was cited as further reason why Pyongyang might attack them.

The North has drawn repeated international rebuke in recent months for threats and actions seen as provocative by the international community. Those include a nuclear test in May and short-range ballistic missile launches on July 4.

North Korea has not responded to the allegations of its involvement in the Web site outages.

The assaults appear to be on the wane. No new similar cyberattacks have been reported in South Korea since Friday evening, according to the state-run Korea Information Security Agency.