Companies that own the application marketplaces say they, too, are on the watch for fraudulent apps. At Apple, the policy is to vet each application before it appears in the App Store. But no system is foolproof. For example, there are apps for so-called jail-broken iPhones, which are unlocked in order to allow the use of other networks besides AT & T or to download applications sold on third-party marketplaces. The practice makes the compromised phones more prone to fraud. Apple spokeswoman Trudy Muller says the company takes security "very seriously and has a great track record of addressing potential vulnerabilities before they can affect users."

Google's Android Market, meanwhile, is considered more open than Apple's App Store and relies on its community to flag fraudulent applications, Moeller says. While Google removes apps that violate its policy, that's only after they have appeared on the company's marketplace, where they could have been downloaded and installed by customers.

"The Android Market content policy clearly states that we do not allow applications on Android Market to identify themselves with third-party marks (of conformity) without permission," a Google spokeswoman says. "If an application violates the content policy, we will remove it from Android Market, and developer accounts will be terminated for repeated violations."

There are a few steps consumers can take to avoid this new type of fraud. You could download your bank's application through its own website. A legitimate application will require you to go through an authentication process to register your phone and create an original user name and password, says Emmett Higdon, a senior analyst with Forrester Research who covers online and mobile financial services.

Or you could use your phone's browser to link directly with your bank's website instead of downloading an application, Moeller says.

Ultimately, it will be up to the banks and wireless companies to detect this type of fraud and keep it from reaching their customers in the first place. "This is part of the natural progression of rolling out a new channel," Higdon says. "We went through this with online banking and will go through this all over again with mobile banking."

This article was reported by Aleksandra Todorova for SmartMoney.