By David Henry and Jim Finkle NEW YORK/BOSTON (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 detected that its web servers used by its site www.ucard.chase.com had been breached in the middle of September. Bank spokesman Michael Fusco said that in the months since the breach was discovered the bank has been investigating to find out exactly which accounts were involved and what pieces of information could have been taken.