Government and commercial computer networks for the US and South Korea were hit with a massive attack--that set records for both countries in terms of duration and reach. The North Korean Government is suspected in the assault. Ultimately, the result of this attack was the temporary inaccessibility of websites for the general public, but the attack may have exposed vulnerabilities and security gaps in government and corporate defenses.
The US government and South Korean officials are looking into whether the attacks originated in North Korea. The attacks began on July 4th--coinciding with the North Korea missile launches and the sanctions imposed by the UN in reaction to those launches.
More information: US: Cyber security and online development