What Ad Blockers Are (and Are Not) Doing

The Web has many types of third-party domains and has a variety of available ad blockers. This work evaluates ad blocking tools for their effectiveness in blocking the retrieval of different categories of third-party content during download of popular websites. The results of this work demonstrate that there is much variation in the effectiveness of current ad blocking tools to prevent requests to different types of third-party domains. Non-configurable tools such as Blur and Disconnect provide only modest blockage of third-party domains in most categories. The tool uBlock generally demonstrates the best default configuration performance. By default, Ghostery provides no protection while Adblock Plus and Adguard provide minimal protection. They must be manually configured to obtain effective protection. The behavior of Adblock Plus is particularly notable as usage data indicates it has an 85% share of the ad blocking tool market. Other results based on network traces suggest that approximately 80% of these Adblock Plus users employ its default configuration. Construction of a "composite" ad blocker reflecting current usage of ad blockers and their configurations shows this composite ad blocker provides only a modest range reduction of 13-34% in the set of third-party domains retrieved in each category relative to not employing any ad blocker.