A major processor of credit and debit cards suspects the fallout from a recent security breach may be worse than it initially believed.

Global Payments Inc. discovered computer hackers may have broken into systems containing personal information about an unspecified number of merchants applying to have their sales processed.

The Atlanta company learned about the stolen merchant data as investigators dug deeper into a heist that stole data from as many as 1.5 million credit card accounts. The breach was first reported in late March.

The company didn't identify the affected merchants in Tuesday's update.

Global Payments plans to send notices to people whose information may have been compromised. The company plans to pay for credit monitoring and identity protection insurance.

Tags: Global Payments, data breach, credit card data, payment processor