NEW YORK / BOSTON , Dec 5 ( Reuters ) - JPMorgan Chase & Co is warning some 465,000 holders of prepaid cash cards issued by the bank that their personal information may have been accessed by hackers who attacked its network in July . The cards were issued for corporations to pay employees and for government agencies to issue tax refunds , unemployment compensation and other benefits . JPMorgan said on Wednesday it had detected that the web servers used by its site www.ucard.chase.com had been breached in the middle of September . It then fixed the issue and reported it to law enforcement . Bank spokesman Michael Fusco said that since the breach was discovered , the bank has been trying to find out exactly which accounts were involved and what information may have been compromised . He declined to discuss how the attackers breached the bank 's network . Fusco said the bank was notifying the cardholders , who account for about 2 percent of its roughly 25 million UCard users , about the breach because it could n't rule out the possibility that their personal information was among the data removed from its servers . The bank typically keeps the personal information of its customers encrypted , or scrambled , as a security precaution . However , during the course of the breach , personal data belonging to those customers had temporarily appeared in plain text in files the computers use to log activity . The bank believes " a small amount " of data was taken , but not critical personal information such as social security numbers , birth dates and email addresses . Cyber criminals covet such data because it can be used to open bank accounts , obtain credit cards and engage in identity theft . Many states require banks to notify customers if they believe there is any chance that such information may have been taken in a breach . The bank is also offering the cardholders a year of free credit - monitoring services . The warning only affects the bank 's UCard users , not holders of debit cards , credit cards or prepaid Liquid cards . Fusco said the bank had not found that any funds were stolen as a result of the breach and that it had no evidence that other crimes have been committed . As a result , it was not issuing replacement cards . The spokesman declined to identify the government agencies and businesses whose customers it had warned about the breach . Officials from the states of Louisiana and Connecticut said the bank notified them this week that personal information of some of their citizens may have been exposed . Louisiana citizens included about 6,000 people who received cards with state income tax refunds , plus 5,300 receiving child support payments and 2,200 receiving unemployment benefits , according to a statement from state Commissioner of Administration Kristy Nichols on Wednesday . Nichols said Louisiana would " hold JP Morgan Chase responsible " for protecting the rights and personal privacy of the citizens . Connecticut Treasurer Denise Nappier said she was " dismayed " that the bank took two and a half months to notify the state of the problem . " JPMorgan Chase has some work to do , not only to assure the holders of its debit cards , but also to restore the state 's confidence in the company 's ability to remain worthy of our continued business , " Nappier said in a statement on Thursday . The bank said it did n't know who was behind the attack , though the Secret Service and FBI were investigating the matter . Businesses and government agencies are increasingly using prepaid cards because they are easier to cash than paper checks . Yet the vast stores of data behind payment cards of all kinds have created new risks . In 2007 , some 41 million credit and debit card numbers from major retailers , including the owner of T.J. Maxx stores , were stolen . In May of this year , U.S. prosecutors said a global cybercrime ring had stolen $ 45 million from banks by hacking into credit card processing firms and withdrawing money from automated teller machines in 27 countries . ( Reporting by David Henry in NEW YORK and Jim Finkle in BOSTON ; Editing by Christopher Cushing and Bernadette Baum ) ;