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Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →On August 15, 2010, a transaction in Bitcoin block 74638 briefly recorded 184,467,440,737.09551616 BTC—about 184.4 billion BTC—because a flaw in transaction-value validation let an overflowing output sum pass a software check. It was a serious exploit, but not a lasting break of Bitcoin’s accepted transaction history: the chain containing the invalid block was overtaken by the valid chain.
What happened in block 74638?
The incident record says the transaction’s total output was 184,467,440,737.09551616 BTC. Two addresses received approximately 92.2 billion BTC each, and the block solver received an additional 0.01 BTC. These were values recorded in a transaction on the branch containing the invalid block—not coins that remained in Bitcoin’s accepted history.
The event is often called Bitcoin’s “biggest hack,” but that label can mislead. The documented issue was an exploit of a transaction-validation bug, not a reported theft from a conventional wallet. The available incident account does not establish the attacker’s identity, motive, or a lasting financial profit.
How did the value overflow bug work?
Bitcoin software checks transaction outputs before accepting a transaction into a block. In this case, the old check failed to handle an output total so large that adding the values overflowed the software’s numeric representation. The invalid total could therefore pass the relevant validation check.
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The blockchain itself did not independently “do the arithmetic wrong.” The failure was in the software rule-checking transaction values. The incident exposed a gap between the intended monetary rules and how that version of the client enforced them.
How did Bitcoin respond?
The warning
At 20:38:33 UTC on August 15, Satoshi Nakamoto sent a warning to the bitcoin mailing list. It pointed to block 74638 and advised users not to trust later transactions until the issue was resolved:
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“*** WARNING *** We are investigating a problem. DO NOT TRUST ANY TRANSACTIONS THAT HAPPENED AFTER 15.08.2010 17:05 UTC (block 74638) until the issue is resolved.”
The two times describe different things: 17:05 UTC is the cutoff named in the warning; 20:38:33 UTC is when the warning was sent.
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The software fix and chain recovery
Within five hours of discovery, a new client release added checks rejecting overflowed output values and any single output above 21 million BTC. Some unpatched nodes continued to follow the chain containing the bad block. The valid chain later overtook it at height 74691, so the overflow transaction was not part of the longest-chain history described in the incident record. The sources do not say every node switched instantly.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Did the incident break Bitcoin’s 21 million limit?
It showed that a software implementation could temporarily accept a transaction violating Bitcoin’s monetary rules. But the invalid issuance did not persist in the chain that prevailed. The distinction is between what one temporary branch recorded and what remained in accepted Bitcoin history: the 184.4-billion-BTC transaction belonged to the former, not the latter.
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Sources
- Satoshi Nakamoto Institute archive, for the contemporaneous warning and its timestamp.
- Bitcoin Wiki: “Value overflow incident”, for the transaction amount, validation failure, corrective checks, and chain recovery details. The page reports a last edit of July 22, 2016.
- Bitcoin Institute: “Bitcoin v0.3.10 – overflow bug emergency fix”, a supporting historical account of the bug and software response.
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