Just who is looking over your shoulder when you browse the internet? This weekend, web users will be given a new tool to shine a light on the commercial organisations which track your every movement online.
Lightbeam, a download produced by Mozilla, the United States free software community behind the popular Firefox browser, is claimed to be a "watershed" moment in the battle for web transparency.
Everyone who browses the internet leaves a digital trail used by advertisers to discover what your interests are. Users who activate Lightbeam will be able to see a real-time visualisation of every site they visit and every third-party that is active on those sites, including commercial organisations which might potentially be sharing your data.
Mozilla wants users who install the Lightbeam add-on to Firefox to crowd-source their data, to produce the first "big picture" view of web tracking, revealing which third parties are most active.
Lightbeam promises a "Wizard of Oz" moment for the web "where users collectively provide a way to pull back the curtains to see its inner workings", Mozilla claimed.
Mark Surman, Mozilla's executive director, said: "It's a stake in the ground in terms of letting people know the ways they are being tracked. At Mozilla, we believe everyone should be in control of their user data and privacy and we want people to make informed decisions about their web experience."
Mozilla already offers users the ability to disable "cookies" - small files that download from websites on to a computer, allowing advertisers to target users based on their online activity.
Lightbeam will reveal the source of the third-party adverts, scripts and images stored on a web page which are linked to servers in other domains. An expanding graph visualises the interactions between the sites a user intentionally visits and the third parties which may not be welcome.
Mozilla had come under "tremendous pressure" from trade bodies over its mission to bring transparency to the web, said Alex Fowler, the company's privacy officer.
The company said it was responding to increased privacy concerns following the revelation that the US National Security Agency had tapped into the servers of internet firms, including Facebook, to track online communication.