The National Intelligence Service(NIS) says North Korea has stolen tens of billions of won worth of cryptocurrencies and aims to loot even more through hacking attempts.

Ruling Democratic Party lawmaker Kim Byung-kee said Monday that the spy agency made the assessment in a report submitted to the National Assembly's Intelligence Committee. 

According to Kim, the spy agency revealed that the North sent malicious emails to South Korea's digital currency exchanges and their members to steal the passwords to their trading accounts last year. This apparently led to tens of billions of won in digital cash being stolen from domestic platforms.

The agency warned there should be "special caution" exercised as the North's hacking attempts are set to continue this year and a wider range of cryptocurrency traders are likely to be targeted.

The NIS said it seeks to tightly seal the nation's online data network and jointly address international hacking crimes with other intelligence agencies around the world.