It seems like organized crime got into crypto arbitrage in Korea[1]. Due to Korea's explosive interest in crypto and strong capital controls, demand would continually exceed supply, so crypto was trading at around 30% premium for the second half of 2017. With so much easy money on the table, it seems normal for organized crime to move in.
[1] https://qz.com/1185524/how-one-korean-trader-used-linkedin-t...