PHILADELPHIA (CBS/AP) — Convenience store giant Wawa Inc. said Tuesday it is responding to reports that hacked information from its customers’ credit cards may be being sold on the dark web. The company said in a news release that customers who may be affected can obtain free credit monitoring and identity theft protection.

“Today, we became aware of reports of criminal attempts to sell some customer payment card information potentially involved in the previous Data Security Incident announced by Wawa on December 19, 2019. We have alerted our payment card processor, payment card brands, and card issuers to heighten fraud monitoring activities to help further protect any customer information. We continue to work closely with federal law enforcement in connection with their ongoing investigation to determine the scope of the disclosure of Wawa-specific customer payment card data,” Wawa said in a statement.

Malware discovered last month affected payment card information and was contained within three days, Wawa said.

Cybersecurity firm Gemini Advisory said information from the Wawa theft began to show up for sale on the dark web this week. Gemini said the data breach ranks among the largest ever, potentially exposing 30 million sets of payment records.

The breach affected all of Pennsylvania-based Wawa’s stores, which stretch along the East Coast.

Police are investigating, and the company has said a forensics firm is conducting an internal investigation.

(© Copyright 2020 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)