An analysis by anti-malware firm McAfee says that attacks against South Korean government and U.S. military Websites most likely came from North Korea. The two nations are technically still at war, following the armistice of July, 1953. McAfee said that it first detected the distributed denial of service (DDoS) attacks on March 04, 2011 from compromised hosts in South Korea. However, McAfee detected evidence of greater sophistication in the March, 2011 attacks, however.
Source: https://threatpost.com/mcafee-fingers-north-korea-attacks-south-korean-sites-070611/75398/