A new joint study from Microsoft, Carnegie Mellon University and University of Pennsylvania that investigated 22,484 sex websites using a tool called "webXray" revealed that 93 per cent of pages track and leak users' data to third-party organisations.
"Tracking on these sites is highly concentrated by a handful of major companies," said the researchers who identified 230 different companies and services tracking users in their sample.
Of non-pornography-specific services, Google tracks 74 per cent of sites, Oracle 24 per cent and Facebook 10 per cent.
Porn-specific trackers in the top 10 are exoClick (40 per cent), JuicyAds (11 per cent), and EroAdvertising (9 per cent).
"The majority of non-pornography companies in the top 10 are based in the US, while the majority of pornography-specific companies are based in Europe," said the study.
The researchers - Elena Maris, Microsoft Research; Timothy Libert, Carnegie Mellon University; and Jennifer Henrichsen, University of Pennsylvania - said they successfully extracted privacy policies for 3,856 sites, 17 per cent of the total.
"The policies were written such that one might need a two-year college education to understand them. The content analysis indicated 44.97 per cent of them expose or suggest a specific gender/sexual identity or interest likely to be linked to the user," said the study to be published in the journal New Media & Society.
The team created a hypothetical profile named "Jack" who decides to view porn on his laptop.
Jack enables "incognito" mode in his browser, assuming his actions are now private. He pulls up a site and scrolls past a small link to a privacy policy. Assuming a site with a privacy policy will protect his personal information, Jack clicks on a video.
"What Jack does not know is that incognito mode only ensures his browsing history is not stored on his computer. The sites he visits, as well as any third-party trackers, may observe and record his online actions," the researchers noted.
These third-parties may even infer Jack's sexual interests from the URLs of the sites he accesses. They might also use what they have decided about these interests for marketing or building a consumer profile. They may even sell the data.
Jack has no idea these third-party data transfers are occurring as he browses videos.
"His assumption that porn websites will protect his information, along with the reassurance of the 'incognito' mode icon on his screen, provide Jack a fundamentally misleading sense of privacy as he consumes porn online," wrote the researchers.
The above hypothetical scenario occurs frequently in reality and is indicative of the widespread data leakage and tracking that can occur on porn sites, they added.
In 2017, Pornhub, one of the largest porn websites, received 28.5 billion visits, with users performing 50,000 searches per second on the site.
Statistics vary as to the amount of overall porn activity on the internet, but a 2017 report indicated porn sites get more visitors each month than Netflix, Amazon, and Twitter combined, and that "30 per cent of all the data transferred across the Internet is porn", with site YouPorn using six times more bandwidth than Hulu.
"While the findings of this study are far from encouraging, we do believe regulatory intervention may have positive outcomes," said the researchers.
( With inputs from IANS )