Kids are back in school and learning things in the classroom. What some parents don't realize is that kids are learning plenty from other students and these days, much of the information being shared is about tech gadgets and what they can do with their smartphones.

Even if parents are keeping a close eye on their child's smartphone, there are many apps they may have downloaded that parents would never suspect as being a problem.

Hidden locker or vault apps are very popular with young kids and teenagers. These apps allow them to store photos, videos, text messages and web searches in a hidden locker that requires a secret code or pin number to open.

Many of these hidden locker apps are disguised as calculators on a smartphone screen. The app even functions as a working calculator but when a specific math equation is entered, the app opens a secret locker where hidden photos, videos and other content is stored. Entering 8+8 will show 16, but enter 8+8+2 and the secret locker opens. The only way to reveal the hidden files is by entering the equation.

Some of the apps even give the user the ability to set up a double-secret equation. If a parent demands the equation to unlock the vault, the child can give them the dummy equation which might reveal another hidden locker with only a few things stored in it.

So the child can show the parent the contents of that locker which may only have a few innocent photos. Parents would not suspect then that there's a second, more secret vault where teenagers have been known to store sexting photos and web searches they don't want to be discovered.

Another app, Hip, or Hide It Pro allows users to disguise the hidden locker as a music player or calculator or hide the app icon all together. Only the user would know how to unlock it.

In 2018 Apple removed one such calculator app from the App Store following a police investigation. When I checked this week I found dozens of similar apps available for free on iPhones and Android devices.