A high-profile North Korean defector has claimed that the country has an army of over 6,000 hackers that are capable of crippling major infrastructure and even kill people.
Speaking exclusively to BBC Click Professor Kim Heung-Kwang spent 20 years teaching computer science at Hamheung Computer Technology University.
Professor Kim managed to escape North Korea in 2004.
He believes that many of his students have now gone on to become involved in North Korea's dangerous hacking task force.
Codenamed 'Bureau 21', it's believed that the hackers were behind the Sony Pictures hack attack which saw the company's entire database leak onto the internet.
The hack did huge financial damage to Sony Pictures and was reportedly in retaliation to the film 'The Interview'.
The Sony Pictures hack reportedly cost the company $15m.
As a result the company had three films leaked before their release as well as email records and personal details belonging to Hollywood actors including George Clooney.
Professor Kim was able to escape from North Korea in 2004 but claims to still have regular contact with officials within the secretive country.
Prof Kim says that North Korea has been making a huge military shift towards online warfare with as much as 20 % of its military budget now devoted to cyber attacks.
"The reason North Korea has been harassing other countries is to demonstrate that North Korea has cyber war capacity," he said.
"Their cyber-attacks could have similar impacts as military attacks, killing people and destroying cities."
The mysterious Stuxnet weapon was used on Iran's Uranian enrichment facilities in 2013
Not only is North Korea developing more complex cyber weapons but Professor Kim believes they already have an incredibly powerful version of the Stuxnet weapon that was used to attack the US and Israel.
Prof Kim said: "[A Stuxnet-style attack] designed to destroy a city has been prepared by North Korea and is a feasible threat."
North Korea hasn't just been implicated in the Sony Pictures attack. In March, 2015 South Korea accused North Korea of being responsible for a hacking attack which stole information from one of the country's Nuclear power plants.
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Prof Kim warned that this could have been much more serious saying: "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."
Journalist Martyn Williams spoke to the BBC urging caution about the capabilities of North Korea suggesting that while serious, these claims are still just theories.
"I think it's important to underline that this is theoretical and possible from non-North Korean hackers too.
"It's conceivable that hackers would try something and lives could be at risk."