This is the largest attack reported so far - affecting more than 76 million household accounts and 7 million small business accounts. The hack began in June, but was not discovered until July.
While hackers gained administrative privileges to 90 servers, there's no evidence that any money or account information was taken. This makes the motive for the attack unclear, and suggests that the attack may have been sponsored by a foreign government. They were able to get applications that run on every JPMorgan computer, prompting the need to change out all those programs, a process that could take months while leaving the system vulnerable.