A South Korean cryptocurrency exchange accidentally sent customers more than 40 billion dollars in bitcoin. The mistake briefly turned some users into multimillionaires. The company had intended to give a small reward of 2,000 won, worth about 1.37 dollars. Instead, it sent 2,000 bitcoins to customers on Friday. The platform Bithumb apologised for the error and detailed the incident. The company said it quickly noticed the mistake and recovered nearly all missing tokens. It restricted trading and…