Bueno, resulta que ya hay unos ejemplos de esto. Copio de la Wikipedia en inglés:
- 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 illegally transfer a large number of bitcoins to himself. He used the exchange's software to nominally sell them all, 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 USD 8,750,000 were affected. ***cotizaba a 17 USD***
- 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 220,000 USD 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 resulted in it being shut down, with paying 49% on customer deposits, leaving more than 78,000 bitcoins (roughly equivalent to 800,000 USD 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 460,000 USD from the company. Bitcoinica was hacked twice in 2012, which led to allegations of neglecting the safety of customers' money and cheating 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 $5.6 million in bitcoin-based debts; this led to allegations of the operation being a Ponzi scheme. In September 2012, it was reported that U.S. Securities and Exchange Commission has started an investigation on the case. ***cotizaba a 8,5 USD***
- In September 2012, Bitfloor, a bitcoin exchange, also reported being hacked, with 24,000 bitcoins (roughly equivalent to 250,000 USD) stolen. As a result, Bitfloor suspended operations. The same month, Bitfloor resumed operations, with its founder saying that he reported the theft to FBI, and that he is planning to repay the victims, though the time frame for such repayment is unclear.
Si hacéis la suma de los bitcoins robados, salen 514.000 + 17.000 + 78.000 + 660.000 + 24.000 = 1.300.000 btc. Esto es más de un 10% de los bitcoins existentes por el momento (unos 11 millones).
Por esto recomiendo a quien tenga bitcoins en los exchanges que se haga un master en almacenamiento seguro de bitcoins, y que a continuación los saque del exchange, antes de que un trabajador (o el propietario) del exchange decida jubilarse y comprarse una isla griega (hacen descuentos).
Por cierto, un robo a gran escala en Mtgox podría provocar suficiente pánico como para tumbar la cotización del bitcoin durante una temporada, y quizá de manera definitiva.