INCHEON (Yonhap News) ― Police on Tuesday busted the nation’s largest known distribution ring of online pornography, allegedly involving a university professor and another man in his 70s.

The arrest comes as police crack down on online distributors of sex videos and other pornography in the wake of a number of brutal sexual offenses against women and children.

Three operators of a local file-sharing service were booked without physical detention on charges of recruiting people to upload porn and pocketing some 200 million won ($177,210) in return, the Incheon Metropolitan Police Agency said.

The suspects set up an exclusive club on a local Webhard service to share sexually explicit files, the police said. The service had around 10,000 members and a million hits, they added.

The members allegedly had to pay around 1,000 won to download each gigabyte of files.

Twelve others, including a university professor, were also booked without detention for allegedly posting around 160,000 items of pornography on the Web site, for payment, the police said. The uploaders allegedly received cash ranging from 30,000 won to 10 million won and free coupons from the Web site operators.