An Illinois based sandwich chain is warning its customers about a possible data breach. Jimmy John's posted a letter on the company's website saying they detected problems at 216 stores between June 16th and September 5th of this year. The Champaign based company says the problem has been contained and customers can use their credit and debit cards securely at Jimmy John's stores. The breach affected a number of stores in the area including locations in Chicago, Naperville, Lombard, and Glen Ellyn.