The March exploit affected Ronin validator nodes for Sky Mavis, the publisher of the popular Axie Infinity game, and the Axie DAO, with attackers stealing some 173,600 ether (ETH) and 25.5 million in USDC. An attacker “used hacked private keys in order to forge fake withdrawals” from the Ronin bridge across two transactions, according to a blog posted at the time.
