Convenience store operator Mapco disclosed this week that hackers compromised its payment card processing systems to steal credit and debit card information belonging to an unknown number of customers.

The cards that were impacted were used to make transactions at Mapco outlets March 19 to 25 and April 14, 15, 20 and 21, according to a company statement (PDF). Mapco, a subsidiary of Delek U.S. Holdings, runs hundreds of convenience stores in seven Southern states.

The statement did no say how the hackers were able to breach the processing systems, and a spokesman told that the company was still investigating.

Customers who believe they've been victimized should contact their bank or card brand and monitor their accounts for suspicious activity.