North Korea has doubled the number of its elite cyber warriors over the past two years and established overseas bases for hacking attacks, a report said Sunday. The Norths cyber war unit now has 5,900 personnel, compared with 3,000 two years ago, the Souths Yonhap news agency said. The communist country operates a hacking unit under its General Bureau of Reconnaissance, which is home to some 1,200 professional hackers, a military source was quoted as saying. North Korean hackers have launched cyber attacks through overseas bases in countries such as China, the source said.