The extent of the breach is unknown. A Wendy's spokesperson told the outlet that "it's not appropriate just yet to speculate," though it appears to have happened at multiple locations.

News of the breach comes after a stronger push from Wendy's to compete with rivals like McDonald's by announcing a four-for-$4 campaign in October. Burger King announced a five-for-$4 deal shortly afterward.

>>Wendy's and Burger King got into a fight on Twitter

Industry experts say fourth-quarter financial outlooks for Wendy's will likely be positive. Analysts project quarterly earnings of 11 cents per share. The company's fourth-quarter results aren't expected until February.

This video includes images from Getty Images.