The attacker, and possible subsequent copycat attackers, used a vulnerability in the project smart contract to mint quadrillions of aBNBc, which they then swapped to various other tokens.
Binance halted trading on aBNBc tokens, as well as on HAY tokens, a stablecoin project that was subsequently exploited. Ankr also tweeted that "We have been in touch with the [decentralized exchanges] and told them to block trading", although decentralized exchanges are typically not supposed to be able to "block trading".
Ankr later blamed the hack on an employee, who they say had inserted malicious code into the protocol that was used to exfiltrate the private key.