Some 1,600 guests at hotels in 10 South Korean cities were secretly filmed and the footage livestreamed online for paying customers.
South Korean police have arrested four men.
Cameras were found hidden in digital TV boxes, wall sockets and hair dryers in 42 rooms in 30 hotels. The footage was sent to a site where more than 4,000 members paid $44.95 to watch.
Police said it did not appear that the hotels were involved.
“There was a similar case in the past where illegal cameras were [secretly installed] and were consistently and secretly watched, but this is the first time the police caught where videos were broadcast live on the internet,” police said in a statement.
South Korea is no stranger to secret videotapings. In 2017, police received more than 6,400 complaints of illegal filming, up from 2,400 in 2012.
Last year, tens of thousands of women protested across the country, under the slogan “My Life is Not Your Porn.”