SAN FRANCISCO – Visa USA says it is investigating a possible security breach at a major U.S. retailer but stressed that no breach had been confirmed as of press time. "Visa USA is examining a possible unauthorized intrusion at a U.S. merchant. The review is still ongoing and no security breach has been found at this time. It's important for cardholders to know they are fully protected against unauthorized purchases with Visa's Zero Liability fraud policy," the card brand said. "As always, Visa encourages cardholders to regularly monitor their accounts through statements, Internet account access and to notify their issuing bank of any unusual activity. Additional consumer security tips are available at www.visa.com." A Visa Security (cams) alert on Jan. 26 was a bit more forthcoming. "Visa Fraud Control has been investigating a possible incident at a U.S. based merchant. This merchant is a large U.S. retailer that has locations nationwide," the cams alert said. The alert said a forensic team had been sent in to check for breaches at the retailer and as of press time had not found any, though the team did find that the retailer had been storing card stripe data on servers at the store level and that many stores had unprotected wireless networks running in many of its stores.