P.F. Chang’s China Bistro Ltd. said Monday that a data breach involving customers’ credit and debit cards affected 33 locations in the continental U.S., although its investigation into the problem is ongoing. The company said the problem has been contained, and it has been securely processing credit and debit card data since June 11, a day after the U.S. Secret Service flagged a possible security problem. It hasn’t been determined whether any specific customer’s data was stolen, P.F. Chang’s added.