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The details of more than 70m JP Morgan clients were stolen in a major security breach, the bank revealed late on Thursday.Names, addresses, phone numbers and emails addresses of about 76m households and 7m small businesses were compromised, though the firm said that only customers who use the websites Chase.com and JPMorganOnline and the apps ChaseMobile and JPMorgan Mobile were affected.In an attempt to reassure its customers, the bank said that there was no evidence that the data breach extended as far as account numbers, Social Security numbers, dates of birth and passwords, adding it had not noticed any unusual customer fraud in the wake of the security lapse."This is really a slap in the face of the American financial services system," Gartner security analyst Avivah Litan was quoted as saying by The Independent."Honestly, this is a crisis point."The bank said it discovered the breach in mid-August but has since determined its servers had been hacked as early as June."We have identified and closed the known access paths," said JP Morgan spokeswoman Patricia Weller.The firm announced it had disabled compromised accounts and reset the passwords of all its technology employees in response to the breach, adding that it had told customers that they were not required to change their passwords or account information.Earlier this year, JP Morgan chief executive Jamie Dimon said that despite spending millions on cybersecurity, the bank spends about $250m each year to prevent online data from being breached, the bank remained worried by the threat posed by hackers.The breach at JP Morgan is the latest in a series of data thefts that have targeted financial institutions and major retailers over the last 12 months.Target saw over 40m credit and debit cards compromised in December after it was victim of a cyber-attack, while 56m debit and credit cards were affected last month as Home Depot said a malicious software had attacked its check-out terminals."You have to be paranoid now. You can't slack off," Litan said. "There is no such thing as data confidentiality anymore. Everything is out there."