A $40 billion typo reaches court — why a windfall in your exchange account is not yours

South Korean exchange Bithumb has won the first two rulings in a set of lawsuits against customers who sold Bitcoin the exchange had credited to them by mistake. The Seoul Central District Court decided for the exchange on Wednesday and Thursday in two of four cases, covering claims of 194 million won (about $140,000) and 5 million won (about $3,600), according to a Chosun Biz report.

The error behind the cases is one of the largest ever recorded at an exchange. On Feb. 6, 2026, Bithumb meant to hand out 620,000 won — roughly $420 at the time — in promotional rewards to 249 users. An employee selected Bitcoin instead of Korean won as the payment unit, and the system credited those accounts with 620,000 BTC, a balance worth more than $40 billion at the time.

Bithumb froze the affected accounts and says it recovered 618,212 BTC, or 99.7% of the mistaken amount. Some users had already sold 1,788 BTC of the credited balances. In March the exchange filed four unjust enrichment suits against users who sold and did not return the proceeds, asking for the cash rather than the coins. Two claims, for about 14.8 million won ($10,700) and 500 million won ($362,000), are still pending. Both decided cases proceeded through service by public notice, because court documents could not be delivered to the defendants by ordinary means.

The part worth sitting with is how the balance could appear at all. South Korea’s Financial Supervisory Service investigated how the exchange could credit customers with Bitcoin it did not hold, and reportedly sent Bithumb an inspection opinion in early August, formally beginning sanctions proceedings. No penalty has been announced. A number in an exchange app is a row in that company’s database — a promise to pay you coins when you ask. It is not the same thing as coins in a wallet whose keys you hold.

So if money you cannot explain ever appears in an account — an airdrop you never claimed, a deposit from nowhere, a promotion that pays a thousand times too much — the calm move is to leave it alone and tell the platform. Selling it does not make it yours. It usually just turns a reversible mistake into a debt with your name on it.