December 5, 2013 - JPMorgan Chase says hackers have compromised its network, putting the personal information of almost 500,000 pre-paid cardholders at risk.

According to Reuters, the bank discovered in September that Web servers used by its UCard Web site had been compromised. The affected cards were used by companies to pay employees and by government agencies to distribute benefits.

Although JPMorgan encrypts customer data, during the breach some information temporarily appeared in plain text, says Reuters. Some data was taken but it is not thought to be critical information such as social security numbers.

The bank says it has no evidence that funds have been stolen so it is not issuing replacement cards but it is contacting affected customers and offering them a year of free credit monitoring. The Secret Service and FBI have also been called in.