In a bid to strengthen and increase its cyber attacks, North Korea has almost doubled the number of its cyber warriors over the past two years, military sources say.
They said about 5,900 hackers were active in North Korea, compared to 3,000 in 2012.
"North Korea operates a hacking unit under its General Bureau of Reconnaissance, which has about 1,200 professional hackers," a source said.
The hackers have been setting up operations in foreign countries, China, in particular.
North Korea tops the list in terms of elite hackers, outpacing even the United States and Japan. The U.S. has about 80,000 people in its cyber operation units, with only 900 elite hackers. Japan has only 90.
Military experts say the North has been stepping up its capabilities in covert operations such as cyber warfare.
It has been training 100 cyber warriors each year. With this in mind, the North opened Mirim University in 1986 and Moranbong University in 1990 on the instructions of former leader Kim Jong-il, to train cyber warriors.
The North has often hacked the websites of South Korean government offices, major banks and even media outlets, which it described as being "hostile" toward the reclusive nation.
To cope with the increasing threats from the North, South Korea has set up its own Cyber Command, equipped with about 400 personnel.
Experts have warned that the North will step up its cyber attacks after the China President Xi Jinping's recent state visit to Seoul.
The North opposed the visit, which was the first time a Chinese leader has visited South Korea ahead of North Korea, one of China's longstanding allies.
In an apparent protest, North Korea fired scud missiles into the East Sea while stepping up contact with Japan over abducted families. Japan has been moving to lift sanctions against North Korea in return for steps toward the eventual return of the abductees.