Citigroup's iPhone app has security issue: Citi

We tend to err on the side of caution and won't use a mobile app that isn't certified by the financial institution involved. It appears that might not even be "safe enough," as on Monday Citigroup revealed that its iPhone app was found to have a security flaw.

The flaw was in the initial version of the app, but it's unclear if the three updates that were released since the app's March 2009 introduction had the issue as well. To update, a user simply needs to go to the App Store on their device and it will indicate an update is required. We've seen some users who are rather lax about this, and even saw one who had 20+ updates stacked up, waiting to be applied.

In this case, the Citi group iPhone app accidentally saved personal account information in a hidden file on users' iPhones. Information that may have been stored included account numbers, bill payments and security access codes. It is unclear if the information was stored in a location a hacker could access, or if the information was unencrypted.

Customers were noted by a letter dated July 20th. Other Citi iPhone apps were unaffected, the company said.

The Citi Mobile app is currently the 11th most popular app in the finance category of the App Store. It allows Citi customers to check their balances, transfer funds and pay bills.