It is possible to steal bitcoins; theft has been documented on numerous occasions. At other times, Bitcoin exchanges have shut down, taking their clients' bitcoins with them. A Wired study showed that 45 percent of Bitcoin exchanges end up closing.
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 illegally to transfer a large number of bitcoins to himself. They used the exchange's software to sell them all nominally, creating a massive "ask" order at any price. Within minutes the price reverted to its correct user-traded value. Accounts with the equivalent of more than US$8,750,000 were affected.
In July 2011, the operator of Bitomat, the third largest Bitcoin exchange, announced that he lost access to his wallet.dat file with about 17,000 bitcoins (roughly equivalent to US$220,000 at that time). He announced that he would sell the service for the missing amount, aiming to use funds from the sale to refund his customers.
In August 2011, MyBitcoin, a now defunct Bitcoin transaction processor, declared that it was hacked, which caused it to be shut down, paying 49% on customer deposits, leaving more than 78,000 bitcoins (equivalent to roughly US$800,000 at that time) unaccounted for.
In early August 2012, a lawsuit was filed in San Francisco court against Bitcoinica — a Bitcoin trading venue — claiming about US$460,000 from the company. Bitcoinica was hacked twice in 2012, which led to allegations that the venue neglected the safety of customers' money and cheated them out of withdrawal requests.
In late August 2012, an operation titled Bitcoin Savings and Trust was shut down by the owner, allegedly leaving around US$5.6 million in Bitcoin-based debts; this led to allegations that the operation was a Ponzi scheme. In September 2012, the U.S. Securities and Exchange Commission had reportedly started an investigation on the case.
In September 2012, Bitfloor, a Bitcoin exchange, also reported being hacked, with 24,000 bitcoins (worth about US$250,000) stolen. As a result, Bitfloor suspended operations. The same month, Bitfloor resumed operations; its founder said that he reported the theft to FBI, and that he…