The logo of Bithumb is seen at its cryptocurrencies exchange in Seoul, South Korea, January 11, 2018. REUTERS/Kim Hong-Ji Purchase Licensing Rights, opens new tabSEOUL, Feb 7 (Reuters) - South Korean cryptocurrency exchange Bithumb said on Saturday it had accidentally given away more than $40 billion worth of bitcoins to customers as promotional rewards, triggering a sharp selloff on the exchange.Bithumb apologised for the mistake, which took place on Friday, and said it had recovered 99.7% of ...