The FTC described the marketplace for mobile applications - dominated by online stores operated by Apple and Google - as a digital danger zone with inadequate oversight. In a report by the FTC's own experts, it said the industry has grown rapidly but failed to ensure the privacy of young consumers is adequately protected. The FTC did not say which or how many companies it was investigating.

Among 400 apps designed for kids examined by the FTC, most failed to inform parents about the types of data the app could gather and who could access it, the report said. Others apps contained advertising that most parents would find objectionable or included links to Facebook, Twitter and other social media services where kids post information about themselves.