The bank discovered the intrusion
The bank discovered the intrusion on its servers in mid-August and has since determined that the breach began as early as June, spokeswoman Patricia Wexler said.
"We have identified and closed the known access paths," she said, declining to elaborate.
She also declined to comment on whether JPMorgan has been able to determine who was behind the cyber attack on its servers.
In response to the data breach, the company has disabled compromised accounts and reset passwords of all its technology employees, Wexler said.
In a post on its Chase.com website, the bank told customers that it doesn't believe they need to change their password or account information. It also noted that customers are not liable for unauthorized transactions when they promptly alert the bank.
The breach is yet another in a series of data thefts that have hit financial firms and major retailers.
Last month, Home Depot said that malicious software lurking in its check-out terminals between April and September affected 56 million debit and credit cards.
