Concerns about credit-card security heightened Friday after a little-known Atlanta company disclosed it had been hit by hackers, potentially exposing hundreds of thousands of account holders to fraud.

The breach at Global Payments Inc. is the latest in a wave of data attacks that have heightened consumer concerns about identity theft. The card industry has been particularly vulnerable to those concerns amid a slew of big breaches in recent years as more Americans choose to pay with plastic rather than cash.

The extent of the breach couldn't be determined and it wasn't immediately clear if cardholders have seen fraudulent transactions. Consumers typically aren't liable for unauthorized purchases made on their cards.

The company declined to say how many cards were at risk, but people familiar with the investigation estimated that it could be hundreds of thousands.

The company said it "identified and self-reported unauthorized access into a portion of its processing system." It added that in early March it "determined that card data may have been accessed."