Cookie Consent Guide

This note is a layman’s guide to how the “block lists” that power adblocking work. A block list contains tens of thousands of rules that govern how a website should be displayed. There are two types of rules. “Filter” rules define what should be blocked. “Exception” rules define what content should be displayed. The most popular block list, “EasyList”, contains tens of thousands of these filters and exceptions.

A filter can be brutally simple and generic, such as /images/ads/ which simply targets the directory images and subdirectory ads often used to store advertising content with the wildcard asterisk character used to tell the adblock software not to show any file from that source. EasyList includes dozens of variations on this rule, e.g. a variety of directories are targeted with / *$image, which would block any image filetype from being loaded.

Or the filter can be more specific, such as ##.top-banner-ad-container which would remove the uppermost ad slot from a website.

The screenshots below are taken from the online version of The Irish Independent newspaper. They show how a handful of rules can strip several ads from the page and dramatically change both the experience for the visitor and the revenue for the publisher.

The right-hand screenshot shows ABP’s display of the elements (in red) that it is removing from the page.

Eyeo (the company that operates Adblock Plus) is deeply involved in supporting the EasyList community that contributes many of these rules. But although filters are drawn from downloaded block lists that are updated by adblocking companies and a community of interest that works with them, a user can easily add their own rules too.

Filters and exceptions can be combined in a single rule. This is useful if, for instance, the adblocker wants to remove ads from a specific source on a website but wants to allow other ads through.

Many filters have been designed to block obvious advertising elements from being loaded from third-party advertising servers, and this has led some publishers to mistakenly believe that native advertising offers a way to defeat the adblockers.

Domain name rotation is another tactic to obfuscate the source of both native and regular advertising content, with some ad rotation networks. Instead of serving ads from a stable third-party server, the advertiser uses an ever-changing rotation of domain names so that ads could come from one domain one minute and another the next.

Unfortunately for both native advertising enthusiasts and networks that rely on the one-trick pony of domain name rotation, adblockers have what amount to nuclear options when they feel that an advertiser or publisher has gone to extreme lengths to evade their rules.

So what about adblock walls? The IAB is currently recommending denial of access to content and publishers across Europe to barricade their content behind adblock walls. But adblockers have been efficiently dealing with these for some time.

Adblock walls mainly depend on detecting the presence of adblocking software by planting “bait” elements on the page that trigger adblocking filters. As a result, the only way to reliably detect adblocking software that is actively evading detection is to check if the actual ads actually loaded.

How PageFair Solves the Problem

PageFair works with major publishers to provide a tamper-proof solution that serves ads to adblockers. It uses a blend of technologies, one of which communicates using a channel to the browser that blocking extensions are unable to monitor or affect. It respects user privacy, limits data consumption, and enforces security by rejecting javascript advertising payloads.

To learn more, read about PageFair’s approach to advertising beyond blocking.

Conclusion

The ongoing battle between adblockers and advertisers continues to evolve as both sides develop new strategies to outsmart the other. Understanding how these systems work is crucial for both publishers and users alike.