Save-mart supermarkets has announced that a possible breach of credit card data was recently discovered. The modesto-based chain says that credit card readers in the self-checkout lanes were tampered with at 19-Lucky Stores, and at the Watsonville Save-Mart. Store officials announced that no known thefts have been discovered, but they advised anyone who used the self-checkout lanes to monitor their credit card activity. The damaged card-readers were replaced.