CitiFinancial provides personal, auto, and home equity loans; CitiFinancial Retail Services provides private-label credit cards for retailers.
Citigroup said there was no reason to think the information had been used inappropriately, nor has it received reports of unauthorized activity. "There is little risk of the accounts being compromised because customers have already received their loans," said Kevin Kessinger, executive VP of Citigroup's global consumer group, in a statement.
Beginning in July, such data will be sent electronically in encrypted form.
The incident is the latest in a string of embarrassing disclosures of losses of computer tapes by companies such as Ameritrade, Bank of America, and Time Warner. In addition, there have been reported cases of customer data being lost or stolen from retailers such as Polo Ralph Lauren and DSW Shoe Warehouse, and from information brokers ChoicePoint and LexisNexis.