South Korea's Bithumb said on Wednesday that serious flaws had left the crypto exchange's internal system susceptible to potential sabotage and failed to prevent an erroneous transfer of more than $40 billion in assets last week. The country's second-largest virtual asset exchange said it accidentally gave away about 620,000 bitcoins to customers during a promotional event, instead of 620,000 won ($426), triggering a 17% slump in bitcoin's price.