Operators of a mobile application on which brothels share the personal information of their customers, including phone numbers, were arrested by police, officials said Friday.

They are accused of violating of the law on personal information protection and the law on punishment of prostitution.

According to the Gyeonggi Nambu Provincial Police, some 6,400 sex work establishments shared information about sex buyers, including some 4.6 million phone numbers, their past records of visiting other brothels, occupations and sexual preferences, through the app from January 2021 to February this year.

Once brothel owners install the app, their customers' phone numbers and memos about them stored on their mobile phones are automatically downloaded to a database through the app. Businesses could then acquire the personal data of potential customers using the app and use it for commercial purposes.

A man in his 40s who developed the app, along with his 15 accomplices, reportedly earned more than 1.8 billion won ($2.3 million) by collecting a monthly fee of 100,000 won from its users. They made profits of up to 300 million won each month.

Private detectives looking into people’s records of sex trafficking on behalf of their spouses or lovers were also among the app’s major users.

The app was also used by voice phishers. One voice phishing gang contacted a number of sex buyers on the app and threatened that they would reveal their secrets to extort money, the police said.

“We are continuing additional investigations into similar apps and private detectives who took advantage of the app,” a police official said.

The police confiscated approximately 1.84 billion won of criminal proceeds. Three of the offenders, including the app developer, were taken into custody for questioning by prosecutors, while the other 12 were booked without physical detention.