While most teenagers spend their summer breaks at camp or on vacation, 13-year-old Daniel Singer has been using his free time to launch an anonymous messaging app for mobile phones.

Called Backdoor, the app taps into a person's Facebook or Google Plus contacts. It then lets a person send an anonymous message to any friends who also have the app.

Singer hopes the free app will hook users by offering up clues about the messenger's identity. The first few clues are free, but people eventually have to pay a small fee to receive additional hints.

"Anonymous interaction is one-sided," Singer said. "But we do believe our app has longevity because unlike other anonymous services, we have clues to even out the playing field."

Singer, who will be a freshman at the Harvard-Westlake School in Studio City this fall, runs Backdoor with his dad Uri. They previously started a website called YouTell.com that allows people to ask questions of their friends and receive anonymous feedback.

According to the younger Singer, he taught himself how to design the app. His dad, chief executive of BB Film Productions, helps him with the business side of the venture.

Messaging apps focused on privacy have become popular in the last few years. Snapchat started the phenomenon with its disappearing photos. Then came Whisper, which allows people to post anonymous messages, and TigerText, which lets people send disappearing texts.

Snapchat and Whisper have become especially popular among teenagers and college students who are less interested in posting every facet of their lives on Facebook or Twitter.

But as with other privacy apps, Backdoor has the potential to be abused. The younger Singer said the company will review any problems submitted where it appears that someone is anonymously harassing other users.

He further assured that people can only receive messages from friends.

"It's one of your Facebook friends, but we won't tell you which one," he said. "My friends say it's better than playing games because of the clues."

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