Story highlights Malicious codes have spread to some computers in military intranet, South Korea says

In March, South Korean officials' smartphones were hacked

(CNN) South Korea is accusing North Korea of hacking its military intranet and leaking confidential information.

The accusation was made Tuesday in a news briefing by South Korea's Defense Ministry spokesman Moon Sang-gyun.

JUST WATCHED Official: N. Korea may be planning missile test Replay More Videos ... MUST WATCH Official: N. Korea may be planning missile test 03:42

"We've identified that malicious codes had spread to some computers in the intranet system," he said.

"The Ministry of National Defense assembled a joint investigation team, and after the investigation, we've confirmed that some military data, including confidential information, was leaked. North Korea is assumed to be behind this," Moon told reporters.

The South Korean military still has not determined what exactly has been leaked, Yonhap News reported , but said it was possible the hack could lead the command to rewrite military operation plans.