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DENVER — Parents of current and former students at Canon City High School say a sexting problem grew for years among students before finally yielding a criminal investigation this week.

The problem, according to administrators and law enforcement, is that students appeared to have successfully hidden evidence using “ghost apps,” which are becoming a growing concern all over the country.

One mother told FOX31 Denver that her daughter, who graduated several years ago, told her that students have been sharing and hiding explicit photos of other students for a long time.

“She just said, when we first moved here, that that’s what they did. That is was like a game,” said the mother, who didn’t want to be identified. “Just basically that girls traded (inappropriate) photos like trading cards.”

The students reportedly used “ghost apps” also known as “photo vaults” to hide the images. Each app is different, but most are disguised as common applications like calculators or sound managers, if a user types in a secret code the app then reveals a hidden screen containing photos, videos and other files. They will even hide other apps installed secretly on the phone.

Mike Harris, who educates students all over the area for the Jeffco CHEEZO unit, says kids everywhere are using the apps to hide and share inappropriate photos. He says sexting is familiar to all, including middle school students.

Related: Find tips from the CHEEZO unit here
Related: Protect Your Kids Online

“80 percent of the kids raise their hands saying they know of somebody (who has sent nude or semi-nude photos),” Harris said. “I’m sure a lot of them, it was even themselves.”

Harris says parents should do their homework, but also know that they can’t focus on just one or two apps.

“There are so many different apps, and there’s going to be a new one tomorrow,” Harris said. “Our kids are the ones that are going to find it.”

Harris says the best advice for parents is to focus less on the apps and more on the phone.

“Number one, they should have parental controls (on the phone),” Harris said. “They should be in the driver’s seat rather than the kids driving technology with their devices.”

He says using parental controls will enable parents to research every app before they let their kids install them.

If you have not set up parental controls and you are not sure what is already on your child’s phone, Harris recommends performing a factory reset to wipe the phone clean and start over.