Fashion retailer Forever 21 reported Tuesday that it suffered a security breach that allowed a hacker to gain unauthorized access to credit card information from a number of the company’s retail locations.

According to Forever 21, a third party group notified the company of the possibility that there was “unauthorized access to data from payment cards that were used at certain Forever 21 stores.” The company then launched its own investigation into the matter and discovered that some customer credit card data may have been exposed.

Forever 21 focused its investigation, for which it retained the help of a “leading security and forensics firm,” on credit card transactions that took place in its retail stores between March and October 2017—though the company noted its investigation is ongoing and it is “too early to provide further details.”

What the company could disclose was that at least some transactions during the timeframe it investigated were exposed. Forever 21 implemented encryption and tokenization solutions in 2015 that are designed to protect transaction data on its point of sales machines in its stores. However, the company admitted that not all of its stores had the security layers in operation during the time of the breach.

For the time being, Forever 21 is not disclosing what locations were affected or how many customers may have had their card compromised. Forever 21 operates more than 815 stores in 57 countries.

“We expect to provide an additional notice as we get further clarity on the specific stores and timeframes that may have been involved,” the company said. The company has not provided any additional resources for consumers to determine if they may have been affected.

In the meantime, Forever 21 is simply advising consumers to monitor their credit card statements to ensure their card has not been compromised. The retailer said consumers should “immediately notify” the card issuer if an unauthorized charge is discovered.

“The latest Forever 21 breach proves how critical it is for retailers and other companies to step up their security, particularly as we enter the holiday shopping season. Just because someone has the right credit card or device doesn't mean it is the legitimate user,” Frances Zelazny, a cybersecurity industry expert and vice president of biometrics security firm BioCatch, told International Business Times.

“In order to avoid this type of situation, I would advise that they encourage the use of mobile payment systems that do not send through any credit card details through the POS, and to exercise hyper vigilance in installing and upgrading POS software that may come in the form of email updates containing malicious links,” she said.

The apparent breach is not the first for Forever 21. The clothing store also suffered from an ongoing breach that occurred over a three-year period at one of the company’s retail locations in California. Nearly 100,000 people were affected by the breach.