Los Angeles-based fashion retailer Forever 21 informed customers last week that some of its payment processing systems had been infected with malware for a period of more than 7 months.

The company learned about the breach in mid-October after being alerted by a third party, and customers were first notified on November 14.

Forever 21 operates over 800 stores in 57 countries around the world, and it’s the 5th largest specialty retailer in the United States. The firm has yet to provide information on which stores are affected. It’s still working on determining if stores outside the U.S. are impacted as they use a different payment processing system, but reassured customers that its website, forever21.com, has not been breached.

According to the retailer, hackers penetrated its systems and installed a piece of malware designed to steal payment card data as it was being routed through point-of-sale (PoS) devices. The company has been using encryption technology to protect sensitive data, but the system was “not always on,” allowing unauthorized access to payment card information.

The company’s investigation revealed that in most cases the malware was only able to collect card numbers, expiration dates and internal verification codes, but cardholder names were also compromised in some instances.

The malware was present on Forever 21 systems between April 3 and November 18, 2017. In some stores the malware was active throughout this period, but some locations were only affected for a few days or several weeks.

“Additionally, Forever 21 stores have a device that keeps a log of completed payment card transaction authorizations,” Forever 21 said in a statement. “When encryption was off, payment card data was being stored in this log. In a group of stores that were involved in this incident, malware was installed on the log devices that was capable of finding payment card data from the logs, so if encryption was off on a POS device prior to April 3, 2017 and that data was still present in the log file at one of these stores, the malware could have found that data.”

This is not the first time Forever 21 has informed customers of a security incident involving payment cards. Back in 2008, the company said nearly 99,000 cards may have been compromised in a series of hacker attacks spanning between 2004 and 2007.

Forever 21 is not the only clothing retailer to disclose a data breach in recent years. Brooks Brothers and Buckle also reported finding malware on their payment systems last year, and Eddie Bauer informed customers of a cyber intrusion in 2016.