The Flash Keyboard app has been downloaded more than 50 million times -- but is capable of some extremely dangerous behaviors.
"It looked like it was a convenient keyboard that had some nice features," said Bill Anderson, chief product officer at mobile security company OptioLabs. "The marketing copy in the app store looked great."
For a while, the app was in the top 20 downloads for the Google Play Store, he added.
"The problem was that it asked for just about every permission that an app could ask for," he said. "It was an especially long list. And surprisingly, most people said yes. But the permissions were so excessive that it turned this thing into a potentially marvelous way to hack phones."