South Korea's intelligence agency informed parliament on Monday that North Korea's theft of virtual currency from the country last year was on the scale of tens of millions of dollars, according to parliamentary sources.

They said the National Intelligence Service also briefed the National Assembly that it is investigating whether North Korea was behind hackers' theft of digital money worth 58 billion yen ($534 million) from Japanese virtual currency exchange Coincheck on Jan. 26.

The NIS said tens of billions of won in cryptocurrency were stolen from South Korea cryptocurrency exchanges last year through North Korean cyberattacks, which partly involved the sending of hacking emails to members of the exchanges.

Yonhap News Agency reported in December that the NIS had secured evidence that North Korea was involved in stealing the personal information of some 30,000 people from Bithumb, South Korea's biggest cryptocurrency exchange, back in June, as well as robbing virtual money at Coinus, another local exchange, in September.

The NIS reportedly confirmed that the same code used by Lazarus, a group accused of being behind the 2014 Sony hack, was used in those cases.

About 3 million South Koreans are estimated to have invested in cryptocurrencies and the country is home to one of the world's biggest private bitcoin exchanges.

On Jan. 30, South Korea began a real-name trading system for cryptocurrencies, banning the use of anonymous bank accounts in transactions to prevent virtual coins from being misused.