MasterCard Inc is investigating a potential security breach related to a third-party vendor and has alerted banks and law enforcement officials, the company said on Friday.
The credit-card processor said the issue involves a company based in the US and is also being reviewed by an independent data-security organization.
MasterCard's announcement comes after a report on a blog called Krebs on Security said that both MasterCard and Visa Inc have been alerting banks across the US about a "massive" breach that may affect more than 10 million cardholders.
"MasterCard is concerned whenever there is any possibility that cardholders could be inconvenienced and we continue to both monitor this event and take steps to safeguard account information," the company said in a statement. "If cardholders have any concerns about their individual accounts, they should contact their issuing financial institution."
MasterCard did not say how many of its cardholders might be affected. Visa representatives did not immediately respond to requests for comment.