Los Angeles (AFP) - A massive sexting ring is rocking a high school in Colorado, with at least 100 students trading nude pictures and posting them on social media, news reports said.

Some of the kids in the photographs were as young as 12, and included eighth graders from the middle school, The New York Times reported.

The students, many of whom are on the football team at Canon City High School, could now face criminal charges, reports said.

The school district announced Wednesday that "a number of our students have engaged in behavior where they take and pass along pictures of themselves that expose private parts of their bodies or their undergarments."

Noting that a "large number" of the high school football team players were implicated int he scandal, the district said it was canceling the high school's last football game of the season.

"Because we can't guarantee that every kid we put out on the field would be clean of this circumstance, we would just rather not put a team out at all," Canon City Schools Superintendent George Welsh told NBC television affiliate KOAA.

Noting it first learned of the behavior on Monday based on anonymous tips and student reports, the district stressed that taking a picture of yourself showing a naked private body part and sending it to another person was a felony.

The same applies if receiving such a picture and forwarding it to another person, or receiving such a picture and retaining possession of it over time.

According to The New York Times, police and the district attorney's office are weighing whether to file child pornography charges -- including felony charges -- against some of the participants.

Students circulated up to 400 lewd photographs, it added.

The police probe is focusing on whether any adults were involved, the school district said.

Students used password-protected "phone vaults," apps that often appear to be simple calculators at first glance, to hide the photos from their parents and school officials.

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"It's been going on for years," one Canon City student told KRDO13, an affiliate of ABC television.

The student said some fellow students, especially girls, had been pressured to take pictures of themselves.

The school administration held an assembly Thursday to warn parents and explain the technology that allows their children to hide photos.

Canon City Sheriff Paul Schultz said the problem extends far beyond the town limits.

"With the new technologies, this is happening everywhere," he said. "Should parents be worried? Absolutely."