A key defector has told the BBC that the capabilities of North Korean hackers could stretch as far as to destroy critical infrastructure and even kill people.
Professor Kim Heung-Kwang, escaped North Korea in 2004 and went on to teach computer science at Hamheung Computer Technology University for 20 years.
He told the BBC Click that the country had around 6,000 trained military hackers and has called for a sustained effort from the international community to prevent North Korea from launching attacks.
Soon after the infamous Sony Pictures hack in November 2014 – attributed to North Korea by the US and other countries – it was circulated that the country had around 1,800 “cyber-warriors”.
But Korean technology expert Martyn Williams emphasised the threat was only “theoretical”.
Kim said former students have gone to work for North Korea’s notorious hacking unit Bureau 121, where they are mostly tasked with espionage and other attacks on other countries.
Many attacks are said to have been aimed specifically at South Korean infrastructure including power plants and banks.
“The size of the cyber-attack agency has increased significantly, and now has approximately 6,000 people,” he said.
He estimated that up to 20 per cent of the regime's military budget is being spent on online operations.
“The reason North Korea has been harassing other countries is to demonstrate that North Korea has cyber war capacity,” he added.
“Their cyber-attacks could have similar impacts as military attacks, killing people and destroying cities.”
Kim warned over malware based on Stuxnet, a cyber-weapon that previously hit Iran in 2010 and is widely attributed to the US and Israel, trying to damage the country’s nuclear centrifuges and derail its nuclear programme.
He said North Korea was building its own version of the cyber-weapon.
“[A Stuxnet-style attack] designed to destroy a city has been prepared by North Korea and is a feasible threat,” Kim said.
Earlier this year, the South Korean government blamed North Korea for a hack on the country’s Hydro and Nuclear Power Plant.
“Although the nuclear plant was not compromised by the attack, if the computer system controlling the nuclear reactor was compromised, the consequences could be unimaginably severe and cause extensive casualties,” Kim said.