Citigroup Inc. on Monday said computer tapes containing account and payment history data, including Social Security numbers, on 3.9 million customers were lost by United Parcel Service Inc.

he disappearance is the latest in a series of reported data breaches involving U.S. companies, including Bank of America Corp. and Time Warner Inc.

New York-based Citigroup said UPS, the world's biggest package carrier, lost the tapes while shipping them to an Experian credit bureau in Texas.

The tapes covered CitiFinancial branch network customers and about 50,000 customers with closed accounts from CitiFinancial Retail Services. Customers of CitiFinancial Auto and CitiFinancial Mortgage are unaffected.

Citigroup, the world's biggest bank, on Saturday mailed a letter to customers about the problem. It said it has received no reports of unauthorized activity, and said there is "little risk" of the accounts being compromised.

"We were moving this using an enhanced security procedure we specified and developed with (UPS)," said Kevin Kessinger, president of Citigroup's North America consumer finance unit, in an interview. "You can imagine how frustrated and disappointed we are that this occurred."

Norman Black, a spokesman for Atlanta-based UPS, said "we sincerely regret that in this case we have not been able to find this package. We did conduct an exhaustive search."

Black said UPS is cooperating with Citigroup, and will "do everything we can to make sure this doesn't happen again."

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