World War 3: Banks preparing defences against INTENSE cyber attacks from North Korea

has been hacking financial networks for years but hacking could intensify as Pyongyang weighs the threat of US military action over its nuclear programme.

have been building after a series of nuclear and missile tests by North Korea and fiery verbal exchanges between President Donald Trump and

According to chief technology officer at cybersecurity firm CrowdStrike, Dmitri Alperovitch, North Korean hackers have stolen hundreds of millions of dollars from banks during the past three years, including a heist in 2016 at Bangladesh Bank.

Mr Alperovitch told the Reuters Cyber Security Summit that banks are concerned Pyongyang’s hackers may become more destructive by using the same type of “wiper” viruses they deployed across South Korea and at Sony Corp’s Hollywood studio.

He said: “The difference between theft and destruction is often a few keystrokes.

According to Mr Alperovitch, North Korean hackers could leverage knowledge about financial networks gathered during cyber heists to disrupt bank operations.

He said his firm has conducted “war game” exercises for several banks.

Security teams at major US banks have shared information on the North Korean cyber threat in recent months, said a second cybersecurity expert familiar with those talks.

The source said “We know they attacked South Korean banks” adding that fears have grown that banks in the United States will be targeted next.

Former US assistant attorney general John Carlin said other firms including defence contractors, retailers and social media companies are also concerned.

He said: “They are thinking ‘Are we going to see an escalation in attacks from North Korea?’”

Cyber expert with Washington’s Centre for Strategic and International Studies Jim Lewis said it is unlikely that North Korea would launch destructive attacks on American banks because of concerns about US retaliation.

Representatives of the top American banking regulators, the US Federal Reserve and the Office of the Comptroller of the Currency, have declined to comment.

Both have ramped up cybersecurity oversight in recent years.

It comes as it was reported earlier this month that hackers working for the North Korean government targeted American power companies in South Korea with spear phishing emails, according to cybersecurity experts.

Secret intelligence documents and photos collected by the US military were among what was stolen from South Korea’s classified information by Pyongyang hackers in September 2016.

The hackers asked their victims to take part in a fundraiser in an email, according to a report by the internet security firm FireEye that was obtained by NBC News.

The targets who downloaded the attached invitation would then invite malware onto their computer network, according to the report.

FireEye thinks that the attacks are a result of the soaring tensions between Pyongyang and Washington following the hermit nation’s ballistic missile tests and nuclear programmes.

A statement from FireEye said: “ linked hackers are among the most prolific nation-state threats, targeting not only the US and South Korea but the global financial system and nations worldwide.”

The North Korean government has repeatedly denied accusations by security researchers and the US government that it has carried out