"We're working on trying to make Paris Hilton famous," joked Andrew Puzder, president and chief executive of CKE Restaurants Inc., which owns the two fast food chains. Puzder said his company's ad agency suggested using Hilton. "She's very appealing to our demographic," which he described as young, hungry guys.

"And it turns out she really loved the burger we wanted her to promote," Puzder said. "We did see her eat a couple of them at the shoot."