South Korea's spy agency said North Korean hackers were behind attacks on cryptocurrency exchanges this year in which some 7.6 billion won ($7 million) worth of cryptocurrencies was stolen, a newspaper reported on Saturday.
Attacks in June included the leaking of personal information from 36,000 accounts from the world's busiest cryptocurrency exchange, Bitthumb, the Chosun Ilbo reported, citing the National Intelligence Service.
Attacks in April and September included the theft of cryptocurrencies from accounts at the exchanges Coinis and Yapizon, now called Youbit.
The 7.6 billion won of stolen cryptocurrencies is now worth about 90 billion won ($82.7 million), Chosun Ilbo reported. It also cited the NIS as saying North Korean hackers had also demanded 6 billion won ($5.5 million) from Bitthumb in return for deleting the leaked personal information.
Another attack on about 10 cryptocurrency exchanges by North Korean hackers in October, using emails containing malware, was thwarted by the Korea Internet Security Agency (KISA), the newspaper reported.
The NIS found that the malware used in hacking the exchanges was made the same way as malware used in hacking Sony Pictures in 2014 and the central bank of Bangladesh in 2016, the Chosun Ilbo reported.
The NIS also said emails used in the attacks used North Korean internet addresses, according to the Chosun Ilbo.
The NIS declined to comment. Representatives for KISA, Bitthumb, Youbit and Coinis could not be reached for comment.