An attacker discovered a race condition in Poloniex's withdrawal processing logic. By submitting multiple concurrent withdrawal requests, the attacker could deplete accounts to negative balances before the system updated withdrawal state, extracting 97 BTC without having that balance.

Digital currency exchange Poloniex, which trades bitcoin and other popular digital currencies such as litecoin, namecoin and dogecoin, has lost 12.3% of its total bitcoin supply in an attack. The exchange took to Bitcoin Forum on 4th March to report it had been compromised by a previously unknown vulnerability in its coding.