Bybit, a Dubai-based crypto exchange, has been hit by hackers resulting in the theft of $1.5bn in Ethereum.Bybit assures its users that their cryptocurrency holdings are safe and has promised to refund all affected customers.The company has called on cybersecurity experts to help recover the stolen funds and is offering a reward of 10% of the recovered amount.The hack is considered to be the largest single digital theft in history and may have been carried out by North Korean state hackers.