Experts warn Pyongyang has active cyber-warfare capabilities and may have aimed them at Sony as vengeance for the film The Interview

Despite its poverty and isolation, North Korea has poured resources into a sophisticated cyber-warfare cell called Bureau 121, defectors from the secretive state revealed as Pyongyang came under the microscope for a crippling hack into computers at Sony Pictures Entertainment.

North Korea has consistently denied it was behind last months attack and subsequent leaks but U.S. officials announced on Wednesday that the hack indeed originated from the Hermit Kingdom.

That means Bureau 121 is back in the spotlight in a major way as the world awaits more details in the coming days about how the unprecedented studio take-down was orchestrated and what U.S. authorities plan to do in response.

Powerful weapon: Jang Se-yul is a defector who trained as one of North Korea's 'cyber warriors' in the country's Bureau 121 hacker cell. He says the North Korea's hackers can launch powerful attacks on the country's enemies

Defectors from the North have said Bureau 121, staffed by some of the most talented computer experts in the insular state, is part of the General Bureau of Reconnaissance, an elite spy agency run by the military. They have said it is involved in state-sponsored hacking, used by the Pyongyang government to spy on or sabotage its enemies.

Pyongyang has active cyber-warfare capabilities, military and software security experts have said. Much of it is targeted at the South, technically still in a state of war with North Korea.

But Pyongyang has made no secret of its hatred of the United States, which was on the South's side in the 1950-53 Korean War.

In North Korea, it's called the Secret War Defector Jang Se-yul

Military hackers are among the most talented, and rewarded, people in North Korea, handpicked and trained from as young as 17, said Jang Se-yul, who studied with them at North Korea's military college for computer science, or the University of Automation, before defecting to the South six years ago.

Speaking to Reuters in Seoul, he said the Bureau 121 unit comprises about 1,800 cyber-warriors, and is considered the elite of the military.

'For them, the strongest weapon is cyber. In North Korea, it's called the Secret War,' Jang said.

One of his friends works in an overseas team of the unit, and is ostensibly an employee of a North Korean trading firm, Jang said. Back home, the friend and his family have been given a large state-allocated apartment in an upscale part of Pyongyang, Jang said.

'No one knows ... his company runs business as usual. That's why what he does is scarier,' Jang said. 'My friend, who belongs to a rural area, could bring all of his family to Pyongyang. Incentives for North Korea's cyber experts are very strong ... they are rich people in Pyongyang.'

North Korean leader Kim Jong Un visits an outpost at Mount Osung Defectors from the North have said Bureau 121, staffed bysome of the most talented computer experts in the insular state,is part of the General Bureau of Reconnaissance, an elite spyagency run by the North Korean military

Slowly advancing: Here, a North Korean student works at a computer terminal inside a computer lab at Kim Il Sung University in Pyongyang. The nation is increasingly online and according to defectors they harbor hackers to attack South Korea and their perceived enemies in the West

Despite its poverty and isolation,North Korea has poured resources into a sophisticatedcyber-warfare cell called Bureau 121, defectors from thesecretive state revealed as Pyongyang came under the microscope fora crippling hack into computers at Sony Pictures Entertainment

U.S. CONNECTS NORTH KOREA TO CYBER ATTACKS A U.S. government source said investigators had determined that North Korea was behind a cyberattack on Sony Pictures as the studio pulled all plans to release its comedy, The Interview, about an assassination attempt on the North Korean leader. Hackers who said they were incensed by the film attacked Sony Corp last month, leaking documents that drew global headlines, and now they have forced an apparently unprecedented change of plans for a major movie release. The United States may officially announce that the North Korean government was behind the attack in the near future, the U.S. government source said. 'The Interview' had been set to debut on December 25, Christmas Day, on thousands of screens. 'Sony has no further release plans for the film,' a Sony spokeswoman said when asked whether the movie would be released later in theaters or as video on demand. Earlier in the day Sony canceled next week's theatrical release, citing decisions by several theater chains to hold off showing the film. Sony came under immediate criticism for the decision. 'With the Sony collapse America has lost its first cyberwar. This is a very, very dangerous precedent,' Tweeted former Republican House of Representatives speaker Newt Gingrich. Advertisement

He said the hackers in Bureau 121 were among the 100 students who graduate from the University of Automation each year after five years of study. Over 2,500 apply for places at the university, which has a campus in Pyongyang, behind barbed wire.

'They are handpicked,' said Kim Heung-kwang, a former computer science professor in North Korea who defected to the South in 2004, referring to the state hackers. 'It is a great honour for them. It is a white-collar job there and people have fantasies about it.'

America has lost its first cyberwar Fmr. House Speaker Newt Gingrich

The technology news site Re/code reported on earlier this month that Sony intends to name North Korea as the source of the attack. But when asked about the Re/code report, a Sony spokeswoman said no announcement from the studio was coming. The company declined comment on Thursday.

Sony Pictures, a unit of Japan's Sony Corp, is the distributor of 'The Interview,' a forthcoming comedy featuring a plot to assassinate North Korean leader Kim Jong Un. North Korea has described the film as an 'act of war'.

Last year, more than 30,000 PCs at South Korean banks and broadcasting companies were hit by a similar attack that cybersecurity researchers widely believe was launched from North Korea.

Months later, the South Korean government's online presence was targeted, with the president's website defaced with a banner reading 'Long live General Kim Jong Un, president of reunification!'

HACKERS TAKE DOWN SONY: CYBER THREATS END 'THE INTERVIEW' Under the threat of terrorist attacks from hackers and with the nation's largest multiplex chains pulling the film from their screens, Sony Pictures Entertainment took the unprecedented step of canceling the Dec. 25 release of the Seth Rogen comedy 'The Interview.' The cancellation announced Wednesday was a startling blow to the Hollywood studio that has been shaken by hacker leaks and intimidations over the last several weeks by an anonymous group calling itself Guardians of Peace. A U.S. official said Wednesday that federal investigators have now connected the Sony hacking to North Korea and may make an announcement in the near future. The official spoke on condition of anonymity because the official was not authorized to openly discuss an ongoing criminal case. Taken down: A poster for the movie The Interview is carried away by a worker after being pulled from a display case at a Carmike Cinemas movie theater Wednesday in Atlanta Sony said it was cancelling 'The Interview' release 'in light of the decision by the majority of our exhibitors not to show the film.' The studio said it respected and shared in the exhibitors' concerns. 'We are deeply saddened at this brazen effort to suppress the distribution of a movie, and in the process do damage to our company, our employees, and the American public,' read the statement. 'We stand by our filmmakers and their right to free expression and are extremely disappointed by this outcome.' Seemingly putting to rest any hope of a delayed theatrical release or a video-on-demand release Sony Pictures spokeswoman Jean Guerin later added: 'Sony Pictures has no further release plans for the film.' A movie theater worker sweeps rain water under a poster for the movie The Interview at the AMC Glendora 12 movie theater in Glendora, California The fallout from the Sony Pictures Entertainment hack that began four weeks ago exploded Tuesday after the shadowy group calling themselves Guardians of Peace escalated their attack beyond corporate espionage and threatened moviegoers with violence reminiscent of the terrorist attacks of September 11, 2001 Sony has said it stands by the makers of The Interview, a comedy about two journalists - James Franco and Seth Rogen - recruited by the CIA to assassinate North Korean leader Kim Jong Un Advertisement

Neither attack was particularly sophisticated, but South Korean authorities said North Korea was to blame, even though 'hacktivist' groups - online activists who hack high-profile targets in order to spread political messages - first appeared to claim responsibility.

Those attacks used rudimentary but effective malware which security researchers later dubbed DarkSeoul.

For them, the strongest weapon is cyber Defector Jang Se-yul

Also known as the DarkSeoul Gang, the hackers have been involved in a five-year spree against South Korean targets, according to a report last year by computer security firm Symantec, which estimated the group included 10 to 50 hackers and described it as 'unique' in its ability to carry out high-profile and damaging attacks over several years.

Some security experts have cast doubt on North Korean involvement in the attack on Sony, citing the publicity-seeking hacktivist style of the attacks. However, the use of an unknown name by the group behind the Sony attacks, 'Guardians of Peace', is similar to previous attacks by the DarkSeoul gang.

It remains unclear if the DarkSeoul gang are outsiders working on behalf of North Korea, or some of Pyongyang's troops in the isolated country's own 'cyber army'.