A computer hardware problem caused more than 800,000 credit card transactions to be double- or triple-billed last week at stores nationwide, including Wal-Mart, officials said. Staci Busby, a spokeswoman for First Data Corp., an electronic payments processor, said Sunday the excess charges on MasterCard and Visa accounts had been reversed. She said she did not know details of the hardware problem.

Busby was unable to say how many customers were affected by the 800,000 transaction errors, but said they involved retailers including Wal-Mart. "Anyone who conducted a transaction with a Visa or Mastercard on March 31 should check their statements," she said...
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