Washington: Adult entertainment sites are using a bug to track user behaviour and serve targeted ads.
Researchers at the University of California San Diego in the US found 485 popular websites exploiting the bug.
The bug allows hackers to see what other sites a user has visited, and to use this information to serve up targeted advertising, reports the Telegraph.
The researchers examined 50,000 popular websites, and discovered that 485 were exploiting the loophole, 63 were making a copy of user`s browsing history, while 46 were found to be ‘hijacking` this history, according to a California University statement.
Adult website YouPorn was the most popular site found to have used the flaw.
"Our study shows that popular Web 2.0 applications like mashups, aggregators and sophisticated ad targeting, are rife with different kinds of privacy-violating flaws," reads the research paper.
The study found that some browsers, such as Google Chrome and Apple Safari, were not susceptible to the flaw.
The most recent version of Mozilla`s Firefox browser also avoids this loophole, while Internet Explorer users need to turn on "private browsing" to avoid the bug.