The credit card company said Friday it has notified law enforcement agencies and issuers of the MasterCard accounts that are potentially at risk. The credit card company only processes transactions — the credit cards are issued to cardholders by banks such as Citibank and also a number of retailers.
MasterCard wouldn't say how many cardholders, banks or issuing companies are affected.
The company advises cardholders who have concerns that they should contact the financial institution that issued their cards.
MasterCard says its own systems have not been compromised.