As many as ten million Visa and MasterCard customers’ accounts may have been compromised as officials continue to investigate what they now believe as one of the largest-known credit card heists in the U.S.

Both Visa and MasterCard have notified banks of the potential breach of security. The banks are in the process of figuring out the affected accounts and contacting customers involved.

Customers are urged to contact their bank if they suspect any suspicious activity with their account.

Visa is assuring customers affected by the breach, that they will not be responsible for fraudulent purchases.

Visa and MasterCard have both confirmed that the breach occurred from a third party vendor, Global Payments, and not their own internal systems. Global Payments, based out of Atlanta, has seen a drop of their shares by 9.1 percent after the news of the breach broke.

Global Payments said they have “identified and self-reported unauthorized access into a portion of its processing system”. Global Payments discovered the breach in credit-card data in March.

The breach does not necessarily mean cardholders cards were used fraudulently, but that their information was accessed.

MasterCard issued a statement saying, “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. If cardholders have any concerns about their individual accounts, they should contact their issuing financial institution.”

Visa also released a statement saying, “Visa, Inc., is aware of a potential data compromise incident at a third party entity affecting card account information from all major card brands. Visa has provided payment card issuers with the affected account numbers so they can take steps to protect consumers through independent fraud monitoring and, if needed, reissuing cards.”

Blogger, Brian Krebs, broke the news of the breach on his blog Krebs on Security.

Krebs told Technology Live, “Law enforcement asked everyone to keep it quiet so as not to disturb investigations. I’m hearing now from two sources that the investigators suspect Dominican street gangs may be involved and that the fraud is focusing mostly on commercial credit and debit card accounts”.

According to Avivah Litan, a security analyst for Gartner research, the breach involved a taxi and parking garage company in New York City. She also stated that a Central American gang gained the information by answering the application’s knowledge-based authentication questions correctly.

For more information on the breach visit:

http://www.mastercard.us

http://usa.visa.com