A defector says that North Korea's hacker army can destroy entire cities

A North Korean defector who worked as a university professor in the country has claimed in an interview with the BBC that North Korea now has over 6,000 hackers.

Professor Kim Heung-Kwang taught science at a university in North Korea for 20 years. But he defected in 2004 and fled the country.

Speaking to the BBC, Professor Kim estimated that up to 20% of North Korea's military spending goes towards Bureau 121, the army unit believed to focus on hacking.

Professor Kim makes some worrying claims about the capabilities of North Korea's hackers. He said that "their cyber-attacks could have similar impacts as military attacks, killing people and destroying cities."

Another claim made in the interview is that North Korea is working to develop its own malware based on Stuxnet. North Korea was named as the country behind the Sony Pictures hack, in which it used modified computer software to hack into Sony Pictures and take over the company's servers. But now Professor Kim Heung-Kwang says that it wants to develop a new type of malware that can target nuclear plants.

It's widely believed that the Stuxnet attack was a joint effort by the US and Israel designed to disrupt Iran's nuclear development. That attack stopped short of actually killing anyone (it only ruined some nuclear equipment), but North Korea might not be so restrained.

It's tricky to verify any claims made about North Korea's hackers because all of the information that we have comes from defectors. They're not always a reliable source. Shin Dong-hyuk, a North Korean who escaped from the country and went on to talk about his life, admitted to changing details of his story.