There have been many incidents where cryptocurrency has been stolen, but the Mt. Gox incident is the largest to date

Mt. Gox was at one time the largest cryptocurrency exchange on the net, facilitating as much as 80% of global bitcoin trades, according to some sources. And then about 850,000 bitcoin suddenly went missing.

At the exchange rate in 2014, when the problem came to light, that many bitcoin were worth about $450 USD. At the time of this writing, with Bitcoin at a high in 2017, that many bitcoin is worth nearly $13 Billion USD. It is possible that a breach that cost Mt. Gox customers a total of about $8,000,000 a few years before, in 2011, had never been properly patched, and that someone had been funneling off bitcoin since then, apparently due to a flaw in the wallet software. Mt. Gox CEO Mark Karpeles has been put on trial in Japan, where Mt. Gox was located, and it is there that the courts are still, at the time of this writing, attempting to settle the dispute. The way that Japanese law currently deals with such matters entitles the shareholders, in this case, the customers of Mt. Gox who had their bitcoin on deposit at the exchange, to the amount that their interest was worth at the time of the incident.

At the early-2014 exchange rate, each Bitcoin was worth less than $500 USD. In 2017, the price of Bitcoin has broken through $7,000 per Bitcoin and in November 2017 is priced around $15,000 per Bitcoin. Obviously, the former Mt. Gox customers are more interested in the current exchange rate rather than the old one. Karpeles, who owned 88% of Mt. Gox as its CEO, has been described as handling the smaller 2011 incident in an extremely negligent fashion, taking the weekend off when the site was still offline, while at other times refusing to delegate necessary tasks to capable employees and ignoring standard procedures for testing and backing-up code before sending it on to customers.

Mt. Gox had already gotten into some hot water in 2013 when US regulators seized about $5,000,000 worth of its US assets due to the fact that it had not filed in any state as a money transmitter. The Japanese courts are currently most interested in whether Karpeles moved millions of dollars worth of customer funds into his personal accounts in the fall of 2013. While any verdict on embezzlement, or possibly other charges, is still pending, it is noteworthy that if the courts decide to only reimburse customers at the 2014 Bitcoin exchange rate, that would leave a huge sum of money still sitting in the Mt. Gox coffers, currently overseen by a court trustee.

According to Reuters, about 980,000 bitcoin have been stolen since the bitcoin blockchain first came into existence, and about 2/3rds of those were lost at Mt. Gox. Advocates for the security of bitcoin and other cryptocurrencies are quick to point out that it was not a security failure in the blockchain that caused the loss of funds, but instead the security gaps at Mt. Gox, which was given permission by customers to hold their private account keys. Private keys unlock wallet and allow funds to pass out of it. If someone else holds your private key, you technically do not own your wallet. Currently, there is no form of deposit insurance for cryptocurrencies that could be compared to FDIC insurance in the US, which protects banking customers from bank failure and fraud up to certain limits.