On 19 June 2011, a security breach of the Mt. Gox bitcoin exchange caused the nominal price of a bitcoin to fraudulently drop to one cent on the Mt. Gox exchange, after a hacker allegedly used credentials from a Mt. Gox auditor’s compromised computer to transfer a large number of bitcoins illegally to himself. He used the exchange’s software to sell them all nominally, creating a massive “ask” order at any price. Within minutes the price corrected to its correct user-traded value. Accounts with the equivalent of more than $8,750,000 were affected. In order to prove that Mt. Gox still had control of the coins, the move of 424,242 bitcoins from “cold storage” to a Mt. Gox address was announced beforehand, and executed in Block 132749.
In October 2011, about two dozen transactions appeared in the block chain (Block 150951) that sent a total of 2,609 BTC to invalid addresses. As no private key could ever be assigned to them, these bitcoins were effectively lost. While the standard client would check for such an error and reject the transactions, nodes on the network would not, exposing a weakness in the protocol.