More than 1,600 guests at hotels in South Korea were being secretly filmed during their stay, police have said.
Four men have been arrested after officers discovered hidden cameras in plug sockets, hairdryer holders and TV boxes in 30 hotels across 10 cities - though the names of the establishments have not been revealed.
According to reports, the footage was being live-streamed to a website with more than 4,000 viewers.
And of these thousands of viewers, 97 were found to be paying a $44.95 (£34) monthly fee to access extra features, including the ability to replay certain live streams.
Police said that between November 2018 and this month, the streaming site brought in more than $6,000 (£4,600).
Four men were arrested after police found hidden cameras in hotels across South Korea. Credit: Pixabay
Speaking to CNN, police said they have uncovered similar incidents in the past but nothing ever quite on this scale.
They said: "There was a similar case in the past where illegal cameras were installed in (hotels) and were consistently and secretly watched, but this is the first time the police caught where videos were broadcast live on the Internet."
South Korea is currently undergoing a spate of illicit online filming, with 6,400 cases being reported to police in 2017, compared to around 2,400 five years earlier.
Last year, thousands of women marched on the streets of Seoul to demand authorities take action and clamp down on the rising trend of revenge porn.
Computer specialist Lee Ji-soo helps rid the internet of footage of women taken without their consent. She told CNN: "The most common things that the clients are saying - and they are quite heartbreaking - are 'I want to die' or 'I cannot leave my house'.
The footage was being live-streamed to thousands of viewers. Credit: Pixabay
"Especially the victims of spy cam or illegally taken videos say that when they encounter people on the street, they feel like they would be recognised."
Speaking to Lonely Planet, Jess Kelly, tech corespondent at Newstalk, offered her advice for spotting hidden devices in rooms,
She said: "It would be nice to think that you never have to worry about hidden cameras when staying in an Airbnb, however, I still find myself looking on bookshelves and above curtain rails every time.
"The big giveaway tends to be a red, blue or green light. Some cameras are motion-sensored, so keep an eye out for a light that just suddenly appears as you walk the room."
But if you're still unsure, Jess says the best thing is to leave and find somewhere else to stay.
She added: "If you feel you are being watched, report and get out."
Featured Image Credit: Pixabay