Cryptocurrency exchange Binance has revealed hackers stole over 7,000 bitcoins worth around $40 million in a single transaction on May 7. It said the affected cryptocurrency wallet contained 2% of total bitcoins that it holds, adding, "All our other wallets are secure and unharmed." Binance is presently world's fourth-largest cryptocurrency exchange, as per coinmarketcap.com data for past 30 days.