A smartphone app allows users to hide photos and contacts that they don't want others to see.

The app, called Private Photo (Calculator%), is just one of many apps that allow people to hide information within their smartphones.

It's been available since 2012, but an Alabama prosecutor's video warning about it has gone viral, upping its exposure. She says parents should be aware that teens and children often use it to keep secrets from their parents and teachers.

Security experts say that the major concern is about who can access the app and whether predators can use it to exploit children.

Experts say that parents should monitor their children's phones and track the apps that they are purchasing.