“Norway has one of the highest digital competencies in the world — 87 percent of children aged 9 to 11 have access to smartphones, and it makes them more vulnerable,” Mr. Steinhovden said. The rate increases to 97 percent for children 12 to 14 years old, according to a report by the Norwegian Media Authority.

“We’re just catching up with the side effects,” he said, “and the debate about whether we should regulate our use, and how we should do it, is just getting started.”

‘It’s the Shame’

In the latest case of catfishing — in which someone adopts a phony online personality to lure others — only two victims initially came forward, despite hundreds of them being identified in videos and via chat logs. One boy spoke to his parents about it, the authorities said, and the mother of another boy figured it out and alerted officials.

Those two complaints spurred an investigation in 2016, which concluded in June. Indictments were handed up this month.

The reluctance of victims to step forward further complicated the case; some have declined to talk to investigators even after police identified hundreds of victims, Ms. Hansson Bull said.

“I think maybe it’s the shame; they’re trying to minimize the case, trying not to tell,” she noted.

Until the police approached them, some victims had not realized they were part of a scam.

“Some victims didn’t even know they were abused, even when they were threatened,” Ms. Hansson Bull said, as the suspect was still pretending to be a girl.