The world already knows that North Korea’s cyberattacks -- like its nuclear bombs and long-range missiles -- pose a serious threat to global security. Yet, the recent hacking of digital currency exchanges show how ill-prepared we are to fight the North’s state-trained hackers.

The National Intelligence Service said last week that it secured evidence that North Korean hackers broke into four cryptocurrency exchanges this year.

It said emails sent by the hackers were traced to North Korean hacking sites and the hackers used the same malicious codes that a North Korean hacking unit planted in attacks on Sony Pictures in 2014 and the Bangladeshi central bank in February this year.

The hackers stole the personal information of about 36,000 customers of Bithumb, the largest cryptocurrency exchange in the country, with which they demanded 6 billion won ($5.5 million) in ransom money. The infiltrators succeeded in stealing bitcoins worth 7.6 billion won from two other digital currency exchanges. The stolen bitcoins are now valued at 90 billion won.

In addition, the NIS said there were attempts to breach about 10 more cryptocurrency exchanges last month alone. This shows that the fast-growing digital currency market has become a major target of North Korean hackers.

It would be strange if the North did not target the market whose value is rapidly increasing, as the country is suffering from a severe shortage of hard currency due to the harshest international sanctions against its nuclear and missile provocations.

Moreover, digital currencies like bitcoin are easier to gain than physical currency. They can be traded anonymously and are easier to launder as well. Intelligence officials said North Korean hackers change the digital currency they steal into US dollars or euros in developing countries and funnel them into North Korean funds.

The latest North Korean cyber heists confirm that the rogue regime is shifting its hacking-for-money operation into higher gear, as it badly needs hard currency in the face of international economic sanctions imposed over its nuclear and missile programs.

In fact, the North Korean hacking units have attempted to breach foreign governments and financial institutions in an increasingly bold and indiscriminate manner. They already stole money from the Bangladeshi central bank and attempted to break into the Bank of Korea and the Federal Reserve Bank of New York.

US intelligence officials believe North Korea earns about $1 billion a year -- a third of its exports -- from cyber heists. This calls for South Korea and the international community to make extra efforts to protect the fast-expanding digital currency market and other financial systems from North Korean hackers.

It is all the more important not to allow loopholes in the ongoing economic sanctions against the North’s nuclear and missile programs.

Equally important is that focusing on blocking the North’s hacking for money should not mean lowering our guard against the North’s overall cyberwarfare.

Intelligence officials said North Korea has been running cyberwarfare units manned by specially trained elite staff since the 1990s. They conduct indiscriminate attacks on foreign governments and institutions, stealing confidential data and intelligence and disrupting computer systems and networks. Many of the attacks have political and military purposes.

For instance, North Korean hackers attacked Sony Pictures in 2014 in response to a film that ridiculed its leader Kim Jong-un.

Last year, North Korean hackers stole classified South Korean military secrets, including the South Korea-US joint wartime operation plan and a contingency plan for taking down the North Korean leadership.

The recent cases show that North Korean hackers are watching for every opportunity to break into our systems. We are in a virtual war and should take countermeasures accordingly.