JP Morgan Chase Breach Affects One 76 Million

You'd think bankers could count.

A cyberattack this summer on JPMorgan Chasecompromised the accounts of 76 million households and seven million small businesses, a tally that dwarfs previous estimates by the bank and puts the intrusion among the largest ever.

The details of the breach — disclosed in a securities filing on Thursday — emerge at a time when consumer confidence in the digital operations of corporate America has already been shaken.Target, Home Depot and a number of other retailers have sustained major data breaches. Last year, the information of 40 million cardholders and 70 million others were compromised at Target, while an attack at Home Depot in September affected 56 million cards.

But unlike retailers, JPMorgan, as the largest bank in the nation, has financial information in its computer systems that goes beyond customers' credit card details and potentially includes more sensitive data.