Who Filters the Filters: Understanding the Growth, Usefulness and Eiciency of Crowdsourced Ad Blocking Peter Snyder Antoine Vastel Benjamin Livshits Brave Soware University of Lille / INRIA Brave Soware / Imperial College USA France London
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[email protected] ABSTRACT 1 INTRODUCTION Ad and tracking blocking extensions are popular tools for improv- As the web has become more popular as a platform for information ing web performance, privacy and aesthetics. Content blocking and application delivery, users have looked for ways to improve the extensions generally rely on lter lists to decide whether a web privacy and performance of their browsing. Such eorts include request is associated with tracking or advertising, and so should popup blockers, hosts.txt les that blackhole suspect domains, be blocked. Millions of web users rely on lter lists to protect their and privacy-preserving proxies (like Privoxy 1) that lter unwanted privacy and improve their browsing experience. content. Currently, the most popular ltering tools are ad-blocking Despite their importance, the growth and health of lter lists are browser extensions, which determine whether to fetch a web re- poorly understood. Filter lists are maintained by a small number of source based on its URL. e most popular ad-blocking extensions contributors who use undocumented heuristics and intuitions to are Adblock Plus 2, uBlock Origin 3 and Ghostery 4, all of which determine what rules should be included. Lists quickly accumulate use lter lists to block unwanted web resources. rules, and rules are rarely removed. As a result, users’ browsing Filter lists play a large and growing role in making the web pleas- experiences are degraded as the number of stale, dead or otherwise ant and useful.