Binance paused withdrawals of Ankr tokens after the cryptocurrency exchange's CEO Changpeng Zhao said the tokens were possibly targeted by hackers.

Ankr told decentralized exchanges to block trading and said it will re-issue the tokens after assessing the situation.

Zhao also said the exchange had frozen about $3 million that hackers moved to the Binance's centralized exchange.

"Initial analysis is developer private key was hacked, and the hacker updated the smart contract to a more malicious one", Zhao tweeted.