A survey carried out by computer science boffins at the University College San Diego amongst the top 50,000 websites on the internet showed that 485 sites or roughly one per cent used a piece of code to spy on the user's browser.
The browser vulnerability allows the website being visited to see a list of all the other websites that the user has been to previously, thereby allowing them to generate better targeted ads or check whether the user has been to rial websites.
Unsurprisingly, adult websites make the bulk of the culprits and the researchers found out that Youporn, which is the 67th most visited website in the UK ahead of other well known names such as John Lewis, Cnet or Ask.com, is the most prominent of them.
63 of the 485 websites attempted to copy the user's browsing history while 46 were found to be "hijacking" the browser's history, potentially deleting competitors' entries.
Using a modern browser like Google Chrome and Apple Safari, will eliminate this issue completely; users of Firefox are urged to upgrade to the latest version while those on Internet Explorer have been advised to turn on "private browsing".
The BBC (opens in new tab) refers to a website called "what the internet knows about you (opens in new tab)" which should tell you what your browser can find about you but the site was down.