Harmony Weighs Rollback After Exploit Mints 4 Billion ONE

Harmony is a sharded proof-of-stake blockchain whose native ONE token is used for transaction fees, staking and governance. The suspected minting exploit raises fresh questions about the network’s security controls and token integrity. Harmony previously suffered a roughly $100 million breach of its Horizon Bridge in June 2022, an episode that left the community debating reimbursement plans and the inflationary impact of issuing additional tokens.

An attacker appeared to exploit the network during Asian trading on Aug. 12, 2026, creating about 4 billion ONE tokens without authorization, equivalent to roughly a quarter of the existing supply. ONE plunged 26% after the transactions were detected. Harmony said it was working with major cryptocurrency exchanges to trace transfers and freeze related funds, while developers prepared a software patch and assessed whether to roll back the blockchain to reverse the unauthorized minting.