SEOUL – A South Korean man was sentenced to 34 years in prison on Thursday as part of the country’s crackdown on Sun. Notorious network Online chat rooms lured young women, including minors, with promises of high-paying jobs before forcing them to use pornography.

Prosecutors said the man, Moon Hyung Wook, opened one of the first such sites in 2015. Mr. Moon, 25, ran a secret members-only chat room under the nickname “GodGod” on the Telegram messenger app, providing more than 3,700 clips. Of illegal pornography, they said.

Mr. Moon, an architectural pioneer who was expelled from his college after his arrest last year, was among the most famous of the hundreds of people police arrested during their investigation. Another chat room operator, his name is Man Chu Ju BinHe was sentenced to 40 years in prison last November.

“The accused caused irreparable harm to his victims through his anti-social crime that undermined human dignity,” Judge Chu Sun-pyo, presiding judge, said of Mr. Moon in his ruling on Thursday. The trial took place in a court district in Andong, in central South Korea.

Mr. Moon was charged in June with forcing 21 young women, including minors, to shoot sexually explicit videos between 2017 and early last year.

Prosecutors said he contacted young women looking for high-paying jobs through social media platforms, then lured them into making sexually explicit videos, promising them to pay them large sums. It also hacked the accounts of women who had uploaded sexually explicit content. Pretending to be a police officer investigating pornography.

Prosecutors said that once he obtained the photos and personal data, he used them to blackmail women, threatening to send the clips to their parents unless victims provided more footage.

Prosecutors demanded life imprisonment for Mr. Moon.

Last December, police said they had investigated 3,500 suspects, most of them men in their twenties or teenagers, as part of their investigation of online chat rooms that served as avenues for sexual exploitation and the distribution of pornography. They arrested 245 of them.

Police also identified 1,100 victims.

The scandal, known in South Korea as the “Nth Room Case,” has caused outrage over the brutal exploitation of young women. And women’s rights groups have staged a sit-in of courts where chatroom operators are on trial, accusing judges of condoning sexual crimes by inflicting what they perceive as light penalties.

On Thursday, outside the Andong court, advocates staged a march to demand the maximum penalty for Mr. Moon.

In recent years, South Korean police have begun cracking down on sexually explicit file-sharing sites as part of international efforts to combat child pornography. With the proliferation of smartphones, they quickly realized that a lot of the illicit trade was moving into online chat rooms on messaging services like Telegram.

Police said they had trouble tracking down Internet chatroom clients because they often use cryptocurrency payments to avoid being caught.