A supply-chain compromise of production infrastructure altered withdrawal-approval logic. No private keys were stolen; the system approved fraudulent withdrawals itself.
Controlling what gets signed is sufficient. Key custody is not the only control that matters.
These are the custody configurations structurally exposed to this kind of event. It describes the failure class, not any individual holder.
Whether your own arrangement sits in one of those groups is the question our Custody Independence Standard is designed to answer, and the four questions in Is your custody setup actually safe? walk through it.
Exchange disclosure, third-party incident analysis
Figures are as reported by the named sources. Proof of Custody has not independently reproduced the underlying analysis.
Proof of Custody, "BigONE" incident record, proofofcustody.io/incidents/bigone-2025A supply-chain compromise of production infrastructure altered withdrawal-approval logic. No private keys were stolen; the system approved fraudulent withdrawals itself. Reported loss: ~$27M.
Controlling what gets signed is sufficient. Key custody is not the only control that matters.
This class of failure could reach: bitcoin left on an exchange. It describes the failure class rather than any individual holder.