The banking apps market for Apple's iPhone devices and other cell phones is exploding. Already, 18 million adults actively use mobile banking, according to Celent, a research firm based in Boston.
But app security is lagging behind.
For example, Citibank said this summer that its iPhone banking app had a security flaw and advised downloading an upgrade. "People think that apps downloaded from the Apple Store are secure," says DeCastro. "But that doesn't mean there won't be issues. More and more people are trying to steal credentials."
Downloading third-party apps not issued by an authorized bank is also dicey. "Download apps you trust," says Mahaffey. To do that, look at app ratings and quality.
"If there aren't many downloads, you want to be careful," says Mahaffey. "Smart phones have the same security issues as PCs. Don't let your guard down."