Citigroup’s free US mobile-banking application for Apple’s iPhone contains a security flaw, leading the bank to advise its customers to upgrade to a newer version that corrects the problem. The Wall Street Journal notes that Citi said its iPhone app accidentally saved information – including account numbers, bill payments and security access codes – in a hidden file on users’ iPhones. The issue affected the approximately 117,600 customers who had registered the iPhone app with Citi since its launch in March 2009.