Bitcoin exchange Youbit to file for bankruptcy after cyber-thieves steal a fifth of its clinents’ holdings

A Bitcoin exchange in South Korea has gone bust after being hacked, pointing to the perils of trying to cash in on this year's stunning boom in digital currencies.

Seoul-based Youbit said it was filing for bankruptcy after cyber-thieves stole around a fifth of its clients' holdings in an attack yesterday.

This is the second time that hackers have targeted Youbit, which allows customers to trade in Bitcoin.

In April, thieves cleaned out 38 billion won ($35 million) in digital currencies, but the company did not say how much was taken in the latest heist or how exactly it happened.

Meanwhile, according to one cybersecurity CEO, companies that deal in Bitcoins and other digital currencies need to be wary of North Korea, which is ''building a cache'' of stolen crypto-loot, says one cybersecurity CEO.

''It's an anonymous currency, it can easily bypass any sort of sanctions because there are none on Bitcoin, and the value has increased dramatically,'' CrowdStrike CEO George Kurtz told CNBC's Squawk Alley yesterday. ''It's the perfect currency for North Korea to be hoarding.''

Kurtz's warning follows a huge increase in the value of Bitcoin this year and the difficulty to trace the currency which is now trading for over $17,000.

Kurtz also addressed the WannaCry cyberattack in which hackers took control of computer systems in 150 countries in May 2017, including those of banks, healthcare companies, and the UK's National Health Service. Trump administration officials confirmed on Monday that North Korea was behind the attack that involved demands that victims pay ransom in bitcoin to regain control of their files.

''We do not make this allegation lightly,'' president Donald Trump's homeland security advisor wrote in a Wall Street Journal op-ed on Monday about North Korea's alleged involvement. ''It is based on evidence. We are not alone with our findings, either. Other governments and private companies agree. The United Kingdom attributes the attack to North Korea, and Microsoft traced the attack to cyber affiliates of the North Korean government.''