Wendy’s, the nationwide chain of fast-food restaurants, says it is investigating claims of a possible credit card breach at some locations. The acknowledgment comes in response to questions from KrebsOnSecurity about banking industry sources who discovered a pattern of fraud on cards that were all recently used at various Wendy’s locations.

Bob Bertini, spokesperson for the Dublin, Ohio-based restauranteur, said the company began receiving reports earlier this month from its payment industry contacts about a potential breach and that Wendy’s has hired a security firm to investigate the claims.

“We have received this month from our payment industry contacts reports of unusual activity involving payment cards at some of our restaurant locations, ” Bertini said. “Reports indicate that fraudulent charges may have occurred elsewhere after the cards were legitimately used at some of our restaurants. We’ve hired a cybersecurity firm and launched a comprehensive and active investigation that’s underway to try to determine the facts.”

Bertini said it was too soon to say whether the incident is contained, how long it may have persisted, or how many stores may be affected.

“We began investigating immediately, and the period of time we’re looking at the incidents is late last year, ” he said. “We know it’s [affecting] some restaurants but it’s not appropriate just yet to speculate on anything in terms of scope.”

When KrebsOnSecurity initially began hearing from banking industry sources about a possible breach at Wendy’s, the reports were coming mainly from financial institutions in the midwest. However, this author has since heard similar reports from banks on the east coast on the United States.

The Wendy’s system includes approximately 6, 500 franchise and company-operated restaurants in the United States and 28 countries and U.S. territories worldwide. Bertini said most of the U.S.-operated stores are franchises.