A bot on the Telegram chat app took fake nude photos of more than 100,000 photos of women.
The bot is still active and the images are shared across different Telegram channels, researcher Sensity.ai discovered.
They are so-called deepfakes, photos that are generated by an artificial intelligence based on existing material.
The number of deepfakes made with the bot increased nearly 200 percent in the past three months.
Users can post pictures of women in the Telegram bot and thus generate a nude photo.
Sensity.ai writes that 70 percent of the cases are photos of women the user knows, not celebrities or politicians.
The program works by identifying clothing and estimating different points of the body underneath.
It then creates a naked body based on that.
Most of the users are from Russia, and the bot also appears to have a presence on the Russian social network UK.
Deepfakes are increasingly difficult to distinguish from real photos.
The vast majority is used as pornography, but in some cases deepfakes are also used to blackmail people or to take revenge on affected women.
Typically, victims of deepfakes have not consented to the use of their material.