It's something you have to know about if your child has a smartphone. Experts say even if you monitor their online activity, follow who they call, and check out who they text, you could be missing something.
Something like a texting app.
Turns out, you can text outside the phone's messaging feature by using special texting applications.
"Parents aren't aware of them, and so kids are using those applications to communicate in a manner that their parents will never ever know about because most parents don't go through every single app," says crimes against children specialist Detective Mike Harris.
Harris says such apps keep the texts from going to the place the would normally go. So, unless you are looking for it, you may not find it.
It's an issue that Harris says puts children in danger.
Members who use some of these apps can chat with each other. That's how a criminal can get access to a child. Harris said it's not uncommon for predators to ask for naked pictures and then it escalates from there.
"Naked pictures are the fuel that gives the predator the stimuli until they can actually meet that live child," he says.
Harris has made more than 500 arrests in the last eight years.
"I'm always amazed, because we aren't arresting people who aren't smart. We are arresting professionals … Businessmen; I've arrested people in law enforcement. It's not just that low element of people that you'd think would commit crimes. These are people in society that no one would imagine," Harris said.
He said the cloak of anonymity that technology offers makes it easier for predators to act on their devious thoughts.
The most common of such texting apps are Text Free, Text Now and Text Plus.
The texting app companies say they are taking steps to protect users.