Harmony Founder: Horizon Attack Caused by Private Key Breach

Harmony founder Stephen Tse tweeted that the attack on Horizon was not due to a smart contract vulnerability, but to a private key compromise. Funds were stolen from the Ethereum side of the cross-chain bridge. Although Harmony stored the private keys encrypted, the attackers decrypted some of them and signed some unauthorized transactions. The stolen assets included $BUSD, $USDC, $ETH, and $WBTC. Harmony has now migrated Horizon's authentication privileges on the Ethereum side to 4/5 multi-signature.