North Korean hackers have reportedly committed cyberattacks throughout the last several months targeting the combined military exercise of South Korea and the United States.

The Gyeonggi Nambu Provincial Police Agency said on Sunday that Kimsuky, a North Korean hacking group, was found to be responsible for the hacking attempts after an investigation into malicious e-mails sent to employees of a South Korean war game operating company in February.

The employees have been dispatched to the combined military exercise battle simulation center since February this year.

Despite the attacks, military-related information was reportedly not stolen as the security system of the U.S. military was activated.

Police have been tracking the senders of the malicious e-mails for about five months after receiving a request from a U.S. military-related agency to cooperate in the investigation in March.

Police believe that Kimsuky committed the cyberattacks in order to steal information and materials from U.S. Forces Korea ahead of the combined exercises.