The Fall of Mt. Gox: How 850,000 BTC Vanished
The full story of crypto's defining disaster — how the exchange that handled 70% of the world's bitcoin trades lost 4% of all BTC, and what it took a decade to unwind.
On 24 February 2014, the website of the world’s largest bitcoin exchange went blank. Within days, Mt. Gox had filed for bankruptcy in Tokyo and disclosed the number that still defines exchange risk: approximately 850,000 BTC missing — about 4% of every bitcoin that will ever exist.
How it got so big
Mt. Gox began in 2007 as Magic: The Gathering Online Exchange — a marketplace for trading digital cards from the Wizards of the Coast game. When founder Jed McCaleb pivoted the order-book code to bitcoin in July 2010, it turned out the infrastructure for trading fantasy cards was almost exactly the infrastructure for trading a brand-new cryptocurrency.
The timing was perfect. Through 2011–2013, as bitcoin climbed from cents to over $1,000, Mt. Gox became the default venue: at its peak it processed roughly 70% of all global BTC/USD trades. French programmer Mark Karpelès, who had bought the exchange from McCaleb in 2011, ran it from Tokyo with a small team and — as later investigations showed — a dangerously casual approach to security.
The slow leak
The collapse was not a single heist. Forensics later established that the exchange had been leaking bitcoin for years: a wallet vulnerability exploited from 2011 onward, hot wallets drained repeatedly, and losses quietly papered over. By late 2013, Mt. Gox was already insolvent — customer deposits were being used to cover holes while the exchange publicly blamed withdrawal delays on “transaction malleability,” a real but minor Bitcoin protocol quirk.
The endgame: in early February 2014, withdrawals stopped entirely. On 24 February the site went dark. A leaked internal document (the “crisis strategy” memo) revealed the true scale of the loss days before the bankruptcy filing made it official.
The numbers
- 850,000 BTC reported missing (~200,000 were later found in an old-format wallet)
- ~$470 million in customer value at 2014 prices — tens of billions at later peaks
- 127,000 creditor claims filed in the bankruptcy
- 10 years until the first rehabilitation payouts began, in July 2024
The aftermath
Karpelès was arrested in 2015 and spent over a year in pre-trial detention. In 2019 he was acquitted of embezzlement and aggravated breach of trust — the court found the evidence insufficient — but convicted of record tampering and given a suspended sentence. The civil side took even longer: Japan’s unusual civil rehabilitation process meant creditors were eventually repaid in yen and bitcoin, with payouts beginning in 2024, a decade after the collapse and after bitcoin had risen more than a hundredfold from its 2014 price.
The lesson, permanently logged
Mt. Gox wrote the industry’s first custody rulebook in reverse. Proof of reserves, cold-storage multisig, segregated customer accounts, and the mantra “not your keys, not your coins” all trace their urgency to that blank Tokyo webpage. Every exchange hack since — Bitfinex 2016, Coincheck 2018, Bybit 2025 — gets measured against it. The difference is that by 2025, a $1.4 billion loss was survivable. In 2014, 850,000 BTC was the whole market’s faith.