“On October 28, 2011 we became aware that some of our customer’s credit card information that was stored on usps.com may have been exposed. The U.S. Postal Service and the U.S. Postal Inspection Service are conducting an investigation into a systems failure on why this happened. Postal Service computer technicians are working around-the-clock to minimize any impact this incident may have caused our customers. The privacy and security of this data is of critical importance to the Postal Service. We apologize for any inconvenience this situation may have caused our customers. About 5400 customers received the letter dated Nov. 8. Testing to fix the situation is going well.”

source: Office Of Inadequate Security: USPS notified 5,400 online store customers after their data were inadvertently revealed to others