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PHILADELPHIA (CBS) — Chili’s Grill & Bar has announced that its payment-related systems have been impacted by a data breach.

Friday’s statement explains that guests who used their card to pay between March and April were likely affected, but they are still working to figure out just how many were impacted by the breach.

Chili’s officials believe that malware was used to gather payment card information, including credit or debit card numbers as well as cardholder names during in-restaurant transactions.

The restaurant’s officials are advising customers to monitor bank and credit card statements for accuracy. If customers notice any suspicious activity, they are urged to contact their bank.

The company confirms that an extensive investigation is underway.