The mastermind behind one of South Korea's biggest online sex abuse rings was sentenced to 40 years in prison on Thursday by the Seoul Central District Court. Cho Ju-bin was found guilty of running a group that widely distributed sexually abusive content he has created by luring and threatening girls into sharing sexual videos in pay-to-view chat rooms.

According to a report from the BBC, at least 74 people including 16 underage girls have been exploited by the group. About 10,000 people have used the chatrooms and reportedly paid up to £1,000 to gain access to the videos. The accused ran a criminal syndicate which he operated throughout secretive chatrooms in the Telegram app.

The girls were said to have been active on chat apps, or Twitter, as they engaged in prostitution or sexting for money. The chatroom operators would usually find girls and contact them with promises of modelling or escort jobs. After extracting personal information, they were blackmailed into doing the videos.

Since investigations began last year, police have arrested 124 suspects and 18 operators for similar sexual crimes that use other social media platforms. The suspects, including Cho, have been detained since.

After Cho's arrest, his case sparked a national outcry in South Korea which brought five million people to sign petitions asking to lift his anonymity. A police committee was pushed to divulge his identity in March. The accused 25-year old college graduate who called himself "The Doctor", once again had tens of thousands signing petitions urging court officials to hand down a stiff prison sentence. This comes as South Korean courts have since been known and accused of leniency towards digital sex criminals.

As judges deliberated on the sentencing, women's rights advocates called for justice to be served as prosecutors sought a life sentence for Cho. The 40-year prison sentence still fell short of what was expected for his crimes.

Although the message of justice after a long fight has been made loud and clear to all South Korean women, women's rights groups still raised concerns regarding victims of such sex crimes. They fear that victims may not get the help they need while sex criminal syndicates continue to receive lighter sentences.

Five other defendants linked to the case have received sentences ranging from seven to 15 years.

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