In a brief statement released Dec. 2, the Bentonville, Ark.-based company said it was alerted to the problem by credit card issuers who reported that customers were complaining of fraudulent charges on their statements.
It's still not clear how the data was obtained, according to the statement. But "electronic systems and databases used inside its stores and for Samsclub.com are not involved," the company said.
Sam's Club is currently working with both Visa International Inc. and MasterCard International Inc. to investigate the breach. The company also has notified the U.S. Attorney's Office for the Western District of Arkansas and the U.S. Secret Service .
Sam's Club officials didn't respond to calls for comment.
In a statement, Visa said it has alerted all of the affected financial institutions, asked them to provide independent fraud-monitoring services to affected customers and requested that they issue new cards as needed.