A lawmaker has uncovered that 1,715 files containing South Korean military secrets, including war plans against North Korea, were stolen from infected Army-issued computers.

Song Young-sun, a member of the South Korean parliament, who sits on the National Defense Committee, asked the Defense Ministry recently to release details about the security breach.

According to the information, the leak occurred between January and March this year, when 13 Army officers who were analyzing sensitive data had their computer infected with unspecified malware.

Apparently the same threat was used in all cases and there are strong reasons to believe that there was a single source for the attacks. Obviously, South Korea suspects the involvement of its Northern neighbor.

According to the military, this is the biggest leak since December 2005, when the country created the CyberSecurity Center to fight against such attacks.

Song Young-sun claims that even though the leaked war plans were old and no longer classified as secrets, they still pose a threat to national security.

"The war operation plans, regardless of the secret-keeping period, can strike a blow to military operations when it gets into the hands of the enemy," the lawmaker told JoongAng Daily, a local newspaper.

"Amid rising tension between the South and the North, the leaking or loss of military secrets by on-duty soldiers can have a serious effect on national security," he added.

South Korean officials are worried about the increasing number of such data breach incidents and also the numerous cases where military personnel are intentionally selling secrets.

In the past we reported that information stealing malware was found on the computer networks of two major South Korean military equipment manufacturers.

One of them, Hyundai Heavy Industries, was tasked with building the country's first AEGIS ships, the King Sejong the Great class of destroyers.