NEW YORK (CBSNewYork) – There’s a new warning for parents to keep a closer eye on their teens’ cellphones, as hidden apps become increasingly popular.

As CBS2’s Reena Roy reported, they could be putting kids in danger.

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Somewhere in the depths of your child’s phone could be a lot more than meets the eye. Apps lurking behind the curtains allow kids to have secret conversations with strangers, send private photos and more.

One of the most popular is Calculator App Lock. At first glance, it appears to be a harmless calculator. But once you type a selected passcode, you enter a secret vault, with hidden photos, videos and notes. It even lets you search the internet in a private browser.

“I have friends that actually use the app before,” high school sophomore Olivia Bala said. “To hide stuff for their parents.”

“They know it’s bad, but they’ll do it anyways,” said high school junior Anthony Alvarado.

There are a lot of these apps out there, like Kik, which allows private messaging with anonymous people, and dating apps specifically for teens, like Yubo, previously called Yellow, which is location-based, plus Hot or Not and Wishbone, where you can rate strangers. On others like Whisper, users can share secrets and post rumors.

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“These apps show that teens are quite savvy with the spectrum of options they have out there,” Digimentors social media strategist Andrew Lih told Roy. “It’s amazing how much power is in the hands of teens now with the mobile phone.”

Lih recommends activating the “Ask to Buy” setting in the App store, which only allows an app download if it’s approved by a parent.

“Read the ratings in the App store and any kind of warnings out there,” he said.

“To see apps like that and they’re easily accessible, it’s kind of scary a bit,” parent Sammy Calixto said. “I’m going to start looking into a little bit more now.”

Another one to keep a closer eye on is Instragram, because on user can make multiple accounts, making activity difficult to track.

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Some apps are also accessible on desktops and iPads, so it’s important to keep an eye on those, as well.