North Korea has doubled the number of government hackers it employed over the last two years according to military sources from the South.
The allegations claim 5900 "elite" personnel were employed in Pyongyang's hacking unit, up from 3000 in 2012.
The hackers had their crosshairs firmly fixed on Seoul but operate from bureaux in China, the source told the Yonhap News Agency.
"The communist country operates a hacking unit under its General Bureau of Reconnaissance, which is home to some 1200 professional hackers," the source told the agency.
The hackers developed and foisted malware against South Korean banks, media websites and government and defence agencies during the employment surge and were fended off by a 900 strong South Korean security blue team.
South Korea in 2013 planned to train 5000 security bods to combat attacks from the North but it was unclear if these personnel have yet been trained.
Pyongyang denied launching attacks and accused Seoul of fueling diplomatic tensions.
The source said the North had more "elite" hackers than the United States with 900, and Japan housing 90.
Pyongyang trained 100 hackers a year through Mirim and Moranbong universities, said to be run by the Government's Operations Department that spearheaded cyber war efforts.
Hackers were divided up into 600 strong brigades taught by Russian professors from the Frunze Military Academy, North Korean defector Jang Se-yul told the popular Seoul Chosun newspaper in 2011.
Intriguingly the same source said in prior years a lack of local facilities meant hackers had to be taught in "faraway locations" including Canada and Australia.
In 2013, North Korea was blamed for distributed denial of service attacks against government agencies including the Presidential Blue House and media companies. It followed much larger attacks in March that year infecting banks, insurance firms and broadcasters with malware that permanently crashed computers. ®