A hacker transfers 25,000 Bitcoins are transferred from 478 accounts on the currency’s largest exchange — Mt. Gox. Mt. Gox admits to a major breach and shuts down.
Karpeles: One account with a lot of coins was compromised and whoever stole it (using a HK based IP to login) first sold all the coins in there, to buy those again just after, and then tried to withdraw the coins. The $1000/day withdraw limit was active for this account and the hacker could only get out with $1000 worth of coins. Apart from this no account was compromised, and nothing was lost. Due to the large impact this had on the Bitcoin market, we will rollback every trade which happened since the big sale, and ensure this account is secure before opening access again.
Within an hour of the hack, 100,000 Bitcoins were sold at incredibly cheap rates on Mt. Gox, plunging the market from around $17.50 USD per Bitcoin to just $0.01 per Bitcoin. Meanwhile 400,000 other Bitcoins are reported missing (approx $8.75M USD at the time). Around the same time a hacker posted the following comment:
I have hacked into mtgox database. Got a huge number of logins password combos.
Mtgox has fixed the problem now. Too late, cause I’ve already got the data. Will sell the database for the right price