Michaels, the biggest U.S. arts and crafts retailer, said on Saturday that it is working with federal law enforcement officials to investigate a possible data breach on its systems that process payment cards. “We are concerned there may have been a data security attack on Michaels that may have affected our customers’ payment card information and we are taking aggressive action to determine the nature and scope of the issue,” Chief Executive Chuck Rubin said in a statement emailed to Reuters.