North Korea runs a cyber warfare unit that tries to hack into US and South Korean military networks to gather confidential information and disrupt service, a news report said Tuesday. The North's military has expanded the unit, staffing it with about 100 personnel, mostly graduates of a Pyongyang university that teaches computer skills, Yonhap news agency reported, citing an intelligence agency it didn't identify. South Korea's Defense Ministry said it is aware that Pyongyang has been training hackers in recent years but did not provide details and had no other comment. The National Intelligence Service - South Korea's main spy agency - said it could not immediately confirm the Yonhap report. The report came a day after the Defense Ministry said it had signed an accord with the Pentagon to strengthen their cooperation in fighting against cyber threats. The ministry statement, however, did not identify any specific cyber threats, such as from North Korea.