A man accused of leading a group that blackmailed girls into sharing sexual videos - which were then posted in pay-to-view chatrooms - has been named after an outcry in South Korea.
At least 10,000 people used the chatrooms, with some paying up to $1,200 (£1,000) for access.
Some 74 people, including 16 underage girls, were exploited.
A police committee took the unusual step of naming Cho Ju-bin, 24, after five million people signed petitions.
"I apologise to those who were hurt by me," Cho said as he was led away from a Seoul police station on Wednesday.
"Thank you for putting a brake on the life of a devil that could not be stopped."
He did not respond when reporters asked if he admitted the charges.
He is accused of abuse, threats and coercion, and of violating the child protection act, the privacy act and the sexual abuse act.
How did the chatrooms work?
As reported by Quartz, customers paid to access the so-called "nth rooms", where extorted content from underage girls was uploaded. Fees ranged from $200 to $1,200.
According to Korean newspaper Kookmin Ilbo, each of the eight "nth rooms" hosted videos from three to four girls who had been blackmailed by chatroom operators.
The girls were active on chat apps, or Twitter, and engaged in prostitution or sexting for money.
The chatroom operators contacted the girls, promising modelling or escort jobs.
They were then directed to a Telegram account where the operator extracted personal details which were used to blackmail them.
Who were the victims?
One schoolgirl - speaking to Kim Hyun Jung on South Korea's CBS radio - said she was approached online after looking for work.
After being promised money and a phone, she was told to send pictures of herself, followed by sexual abuse videos.
The victim said there were at least 40 videos in total.
"He already had my face, my voice, my personal information," the victim said.
"I was afraid that he would threaten me with that information if I said I would quit."
'The fury will not stop here'
Angry South Koreans don't just have a name - they now know the face of the man who allegedly called himself "The Doctor".
His comments outside the Seoul police station will have done nothing to quell the deep wave of anger sweeping through supporters of women's rights in the country.
More than two million signed a petition to have Cho's identity made public. They got their wish. But the fury will not stop there.
Over and over again women have told me they feel the justice system does not adequately punish sex crimes and does not act as a deterrent.
And over and over again tens of thousands of women have urged the current administration to act.
This became apparent during South Korea's so called spy camera demonstrations.
Large-scale protests were held over several weeks at the authorities' lack of action over illicit videos - taken in places such as public toilets and changing rooms - and posted online.
The Minister for Gender Equality Lee Jung-ok has vowed to revise the laws governing sex crimes including online grooming and the blackmail of children and teenagers.
But will the changes go far enough in a country where being drunk is a defence for rape?
The level of outrage at this case should be a warning to the current administration that women in this country are watching closely - and will not wait forever for well overdue reforms.
What was the public reaction?
Details emerged via a newspaper report in November, followed by another report in March.
The story caused outrage in a country where another abuse scandal - the Burning Sun case - dominated headlines last year.
A petition on the presidential website, calling for the main suspect to be named, was signed 2.6m times.
Another petition on the same site, calling for all chatroom users to be named, was signed almost 2m times.
President Moon Jae-in regarded the chatrooms as a "cruel act that destroyed lives", according to a spokesman.
"The fact that more than three million people signed the petition...is a serious plea to the government from the people, especially women, requesting a stop to such malicious digital sex crimes," the spokesman added.
Who else has been arrested?
The National Police Agency told reporters that 124 suspects had been arrested - with 18 chat room operators in custody - since September. Cho is one of the 18.
A user called GodGod, who is suspected of first creating the chat room, remains at large.
"Through strict investigation, the police will entirely transform the social apathy to digital sex crime and strongly root out such crime from our society," said Min Gap-ryong, commissioner general of the Korean National Police Agency.