A computer hardware problem at payments processor First Data resulted in double and triple billing of the cardholder accounts of shoppers at Wal-Mart stores last week.
The charges, which affected some 800,000 Visa and MasterCard debit and credit card transactions on 31 March, have since been corrected, says First Data.
The vendor has opened a toll-free customer hotline to assist consumers.
Wal-Mart is urging any customers who conducted a transaction on 31 March to check their card statements.
Seperately, First Data has announced that it is revising its 2004 EPS guidance upward by $0.17 to a range of $2.17 to $2.35. The change is due to the gain that resulted from the March sale of the company's 67% ownership interest in GCA.