This happens without reading actual requests, thus providing more privacy. The declarative approach utilizes declarativeNetRequest API to preemptively instruct browsers what needs to be blocked. It works by reading every request that a browser is making and deciding on the fly if it represents an ad and should be blocked. Request interception utilizes webRequest API, which is the most privacy violating technique. To plug into browser networking, ad blockers will intercept requests as they happen or use declarative blocking rules defined beforehand. Instead of rendering elements on a page and then hiding them, extensions block the resources on a browser networking level. Resource blocking employs a different technique.Element hiding is done either by injecting CSS code, or by using DOM APIs such as querySelectorAll or removeChild.The first one is element hiding and the second one is resource blocking: There are two ways ad blockers can block content. Google Chrome and other Chromium-based browsers: Extensions are JavaScript applications that run in a sandboxed environment with additional browser APIs available only to browser extensions.In this section we’ll go fairly deep into the internals of ad blockers as it will help us build a better understanding of how ad blocking mechanics make it possible to reliably identify visitors.Īd blockers typically run as extensions built on top of browser APIs: Safari is an exception which we’ll discuss below. Therefore, it is possible for ad blockers to violate user privacy. They have a lot more information about browsing activity than trackers, because trackers can’t do reliable cross-site tracking. However, ad blockers have access to the content of all pages that a browser loads. Privacy conscious users often turn to ad blockers to stop their browsing history from being shared with these platforms. All major online ad platforms (like Google and Facebook), as well as other marketing and product testing tools (like Crazy Egg and Hotjar) use tracking scripts to monitor and monetize user activity online. What is an ad blockerĪn ad blocker is a browser extension that prevents browsers from loading video and displaying advertisements, pop-ups, tracking pixels and other third-party scripts.Īd blockers not only improve the online experience by hiding ads, but also protect browsing activity from being tracked by third-party scripts. We hope shining a light on this cutting edge technique will be useful to the open source community at large. As the developers of the largest open source browser fingerprinting library, we have only started including ad blocker signals as of April 2021, so this work is hot off the press from our team. While browser fingerprinting is a proven-out method of visitor identification (you can read more about how it works in our beginner’s guide), how ad blockers can be used for fingerprinting is rarely discussed. This combining of browser signals to create a unique identifier is known as browser fingerprinting. These discrepancies provide a source of entropy that when combined with other unique signals, can identify a specific user over multiple visits. By testing whether certain page elements are blocked, a site can find discrepancies in the filters used by your specific ad blocker(s). If you are reading this article on ad blocker technology, you almost undoubtedly have one installed.Īd blockers leave a trace that can be harnessed by the websites you visit to identify you. Around 26% of Americans use an ad blocker today. This novel browser fingerprinting method, while oft-discussed as a theoretical source of entropy, has only just been added to Fingerprint as of April 2021, and has never been fully described until now.Īd blockers are an incredibly pervasive and useful piece of technology. In this article, we show how signals generated by the use of an ad blocker can improve browser fingerprinting accuracy. Editor's note: we have made some changes to the article introduction for tone and clarity.
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