NEW YORK (AP) — Sonic says there's been some "unusual activity" on credit cards used at some of its restaurants.

The fast food chain said in a statement that its credit card processor told them about the incident last week and that it's now "working to understand the nature and scope of this issue." It did not disclose how many credit cards were potentially involved in the incident or when the incident took place.

Locally, Sonic has several locations in Shawnee and one in Tecumseh, but there are more than 3,500 Sonic restaurants in 44 states, according to the company's website.

Sonic said that it is working with third-party forensic experts and law enforcement officials on the incident. The potential breach at Sonic was initially reported by Krebs on Security.

Sonic, based in Oklahoma City, is not the first restaurant operator to deal with such issues. Last year Wendy's announced that hackers were able to steal customers' credit and debit card information at more than 1,000 of its U.S. locations. Wendy's said at the time that the hackers were able to obtain card numbers, names, expiration dates and codes on the card. Some customers' cards were used to make fraudulent purchases at other stores.

The News-Star contacted Sonic Wednesday and received this statement:

“The security of our guests’ information is very important to SONIC.  We are working to understand the nature and scope of this issue, as we know how important this is to our guests.  We immediately engaged third-party forensic experts and law enforcement when we heard from our processor. While law enforcement limits the information we can share, we will communicate additional information as we are able.”