Chipotle Mexican Grill said today it has identified what was responsible for the payment card security incident reported April 25. The information comes at the completion of an investigation that involved leading cyber security firms, law enforcement and the payment card networks, according to a company press release.

It identified the operation of malware designed to access payment card data from cards used on point-of-sale (POS) devices at certain Chipotle and Pizzeria Locale restaurants between March 24and April 18, 2017. The malware searched for track data, which sometimes has cardholder name in addition to card number, expiration date and internal verification code, read from the magnetic stripe of a payment card as it was being routed through the POS device.

There is no indication that other customer information was affected, according to the release. Lists of affected Chipotle and Pizzeria Locale restaurant locations and specific time frames are available at www.chipotle.com/security and www.pizzerialocale.com/security, respectively. Not all locations were involved, and the specific time frames vary by location.

Customers who used a payment card at an affected location during its at-risk time frame should remain vigilant to the possibility of fraud by reviewing their payment card statements for any unauthorized activity, according to the company. Customers should immediately report any unauthorized charges to their card issuer because payment card rules generally provide that cardholders are not responsible for unauthorized charges reported in a timely manner. The phone number to call is usually on the back of the payment card.

During the investigation, Chipotle removed the malware and continues to work with cyber security firms to evaluate ways to enhance its security measures. In addition, Chipotle continues to support law enforcement's investigation and is working with the payment card networks so that the banks that issue payment cards can be made aware and initiate heightened monitoring.