During the outage March 20, skulls popped up on some computer screens, which the Korean Internet Agency said indicated hackers had installed malicious code in the networks.
The South Korean National Police Agency said three broadcasters -- KBS, MBC and YTN -- three banks -- Shinhan, Nonghyup and Jeju -- and two insurance firms had reported their computer systems suddenly stopped, the Yonhap News Agency reported.
The South Korean government accused North Korea of orchestrating the attack by putting malicious code in at least six computers that accessed South Korean networks at least 1,590 times since June, Yonhap reported.
"An analysis of cyber terror access logs, malicious code and North Korean intelligence showed that the attack methods were similar to those used by the North's Reconnaissance General Bureau, which has led hacking attacks against South Korea," said Lee Seung-won, an official at the Ministry of Science, ICT & Future Planning.
North Korea has denied allegations it was responsible for the attack, though it has been blamed for similar cyberattacks on South Korean government agencies and financial institutions over the past few years, Yonhap said.