Tor network research raised an early alarm on mass-scale child sexual abuse material distribution and usage
A scientific article published in 2024 in Nature Scientific Reports warned of a growing epidemic of child sexual abuse material (CSAM) distribution on the Tor network.
The article received 340,967 downloads in 2024, placing it as one of the most downloaded scientific articles published in Scientific Reports under Nature Portfolio.
The first writer of the article is Postdoctoral Research Fellow Juha Nurmi from Tampere University.
In the study, researchers analyzed over 176,000 onion domains operating on Tor between 2018 and 2023. They revealed that by 2023, 20% of all onion sites were hosting CSAM. Even more alarming, 21 of the 26 most-used Tor search engines openly provided access to CSAM — and four promoted it directly on their landing pages. The study also found that 11% of search queries on Tor were from users actively seeking CSAM.
Urgent call for law enforcement action and public health interventions
Nurmi comments that researchers criticized the computer science community for neglecting the CSAM problem in anonymous networks, stating that there is a growing global epidemic of CSAM usage and warning that many papers on privacy tools like Tor do not even mention the problem.
“We called for technical reform of anonymous systems and the creation of public health programs for CSAM users,” Nurmi says.
A year later, a massive international law enforcement operation underscored the seriousness of the researchers' findings. On April 2, 2025, Europol announced the seizure of Kidflix, an illicit subscription-based CSAM platform operating on the Tor network. Styled like a dark version of Netflix, Kidflix offered a streaming library of 72,000 CSAM videos and boasted 1.8 million user accounts worldwide. Europol coordinated with multiple national agencies to shut down the service and arrest suspects linked to its operation and distribution networks.
Kidflix’s scale stunned even seasoned investigators, reinforcing the study’s urgent call for both law enforcement action and public health interventions.
“While law enforcement agencies can target specific platforms, like Kidflix, we researchers stress that systemic changes to anonymity technologies — and support for users who want to stop offending — are essential for addressing the problem long-term,” Nurmi says.
SafeHorizon EU project continues the work
Researchers' SafeHorizon EU project continues the work: SafeHorizon is monitoring CSAM distribution on the dark web and clear web, reporting the links to law enforcement, and adding novel techniques to address the problem.
In 2025, the project detected 50,000 onion domains on the Tor anonymity network that disseminate CSAM and reported these to law enforcement.
The original article: Nurmi, J., Paju, A., Brumley, B.B. et al. Investigating child sexual abuse material availability, searches, and users on the anonymous Tor network for a public health intervention strategy. Sci Rep 14, 7849 (2024). DOI: 10.1038/s41598-024-58346-7
