South Korea's military says computer hackers who may be from North Korea have gained access to a secret U.S.-South Korean plan to defend the peninsula if war breaks out.
The South's military says hackers gained access to an 11-page file that was used to brief military officials on the plan, which is called Operation Plan 5027.
The plan calls for the dispatch of nearly 700,000 U.S. troops to the peninsula should a full-scale war break out.
The U.S. military already stations 28,500 of its troops in the South to deter any potential North Korean aggression.
Officials say the suspected hacking occurred late last month when a South Korean officer failed to remove a USB device from a military computer before switching from a restricted-access intranet to the Internet.
They say Pyongyang may have been involved in the hacking attack which used a Chinese Internet or IP address.
The latest case came months after hackers launched cyberattacks that caused Web outages on prominent government-run sites in the U.S. and South Korea.
Affected sites include those of the White House and the South's presidential Blue House.
The Internet address that triggered the Web attacks in July was traced back to an IP location in China that was being leased by North Korea's Ministry of Post and Telecommunications.
At the time, South Korean media reported that North Korea runs an Internet warfare unit that tries to hack into U.S. and South Korean military networks to gather confidential information and disrupt service. Media reports estimate that Pyongyang has between 500 and 1,000 hacking specialists.
Some information for this report was provided by AP, AFP and Reuters.