Summary: Nearly 4,000 BTC worth about $320 million were paid out from the Liquid Bitcoin sidechain's federation wallet on September 6. The striking part is not just the amount: Liquid and SideSwap say the relevant keys were not stolen. The combination of a valid peg-out authorisation, apparently invalidly created L-BTC and a correctly signed Bitcoin payout points to a deeper failure than a conventional key compromise.
Liquid has largely halted network activity and exchanges were asked to suspend L-BTC deposits and withdrawals. The party behind the withdrawal calls itself “whitehats” and has since said it intends to return most of the bitcoin after a fix. That description is not independently verified; at the time of the latest on-chain analysis, the roughly 4,000 BTC were still sitting unmoved at the destination address.
Confirmed
Reuters and Liquid put the withdrawal at roughly 4,000 of the approximately 4,200 BTC previously held in the federation wallet. The payout went through SideSwap, an authorised peg-out provider. Liquid explicitly stated that the Peg-out Authorization Key used for the transaction had not been compromised.
The Bitcoin transaction was therefore not simply an unauthorised wallet spend using a stolen key. Bitquery reconstructed the sequence across Bitcoin and Liquid: the federation regularly signed a 3,996 BTC peg-out after SideSwap submitted a formally valid request. The critical failure appears to have happened earlier in the chain.
SideSwap later said Blockstream traced the underlying problem to a bug in the Elements software. According to that account, roughly 4,000 L-BTC had been created without corresponding newly deposited bitcoin. Blockstream has not yet published a complete technical postmortem, so the exact root cause is not fully verified in public.
The mosaic: every key works, yet the reserve is drained
This is what makes the incident more interesting than a normal crypto-wallet compromise. Liquid is designed around a one-to-one peg: L-BTC on the sidechain should correspond to bitcoin held by the federation. But if a flaw at the asset or consensus layer lets additional L-BTC be treated as valid, a later peg-out can be correctly authorised and still release real bitcoin against value that should never have existed.
Bitquery calculated that roughly 197 BTC remained in the observed peg wallet after the incident. At the same time, around 3,998.5 BTC were still sitting at the address controlled by the self-described whitehats. That means the final financial loss remains uncertain: if the funds are returned, the permanent loss could be far below $320 million. The architectural failure would remain.
The key distinction is simple: key security protects the authorisation layer. It cannot protect a system that has already accepted an economically invalid state as legitimate. A peg-out can then be cryptographically correct while being economically wrong.
Why “Bitcoin was hacked” would also be wrong
The incident affects Liquid, a federated Bitcoin sidechain developed by Blockstream, not Bitcoin's own consensus. Liquid uses a group of functionaries to sign blocks and manage the bitcoin backing L-BTC. The event therefore illustrates a risk of additional protocol layers: more functionality and faster settlement also introduce more state, validation logic and trust assumptions.
That does not automatically make Liquid less secure than every alternative. It does mean its security is not inherited from Bitcoin alone. The federation, Elements, peg-in and peg-out logic, and authorised service providers together form a separate security boundary.
The claimed whitehat changes the situation, not the assessment
Blockstream and the counterparty are now communicating publicly through OP_RETURN messages on Bitcoin. The counterparty first demanded a fix and said it would return most of the bitcoin. Blockstream later replied with a PGP-signed message saying the bridge nodes had been patched and the funds were safe to return.
That is encouraging, but it is not yet a return of funds. Calling oneself a whitehat also proves neither identity nor motive. From a technical perspective, the more important fact is that a single apparent flaw was sufficient to put almost the entire bitcoin reserve behind the peg into motion.
What argues against this interpretation
A complete technical report from Blockstream is still missing. Bitquery can trace transactions and anomalous L-BTC outputs, but Liquid's confidential amounts limit what can be reconstructed externally. SideSwap's description of an Elements bug should therefore not be treated as a final root-cause report.
The financial damage may also be largely reversible if the bitcoin is returned as promised. That would still leave the central technical question unanswered: why could the federation accept such a large, formally valid peg-out in the first place?
Pandorex Analysis
The $320 million figure is the spectacular part. The architecture is the more important part: according to the parties involved, the peg-out key remained intact, yet the reserve could still be almost emptied. That changes the security question from “Who owns the key?” to “Which states is a correctly signed system allowed to accept?”
Pandorex assessment: It is very likely that the core failure was not conventional key theft but faulty validation or asset creation before the peg-out. The on-chain record and SideSwap's account fit that explanation, but a final assessment should wait for Blockstream's complete technical report.