New York (CNN Business) Binance, a major cryptocurrency exchange, says hackers stole more than $40 million worth of bitcoin from its customers.

The Taiwan-based company, one of the world's largest crypto exchanges, announced that it discovered a "large scale security breach" Tuesday. It said hackers stole 7,000 bitcoins in one transaction. One bitcoin trades at nearly $6,000.

"The hackers used a variety of techniques, including phishing, viruses and other attacks," CEO Changpeng Zhao wrote in the statement. He said the company continues to investigate the breach.

Zhao explained that the hackers waited for the best time to conduct their operation, but he didn't clarify specifically how the hack went undetected.

"The transaction is structured in a way that passed our existing security checks," he said. "Once executed, the withdrawal triggered various alarms in our system. We stopped all withdrawals immediately after that."

Read More