Citigroup is advising its customers to upgrade their iPhone app due to a recently discovered security flaw.

"A prominent iPhone security researcher said it would be trivial for someone to access the hidden file if they obtained a lost or stolen phone," writes Computerworld's Gregg Keizer.

"In a letter to customers, the U.S. banking giant said its Citi Mobile app saved banking information -- possibly including account numbers, bill payments and access codes -- in a hidden file on the iPhone," Keizer writes.

Click here to read the Computerworld article.