Adblock circumvention: How it works, why it failed, and what’s next



September 11, 2023

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If you’re interested in ad block recovery, you’ve probably heard about ad block circumvention. Despite being the first mainstream ad block recovery method, it’s now only used by a select few publishers. The reason behind ad block circumvention’s decline is simple: it requires massive resources to be sustainable. For ad block circumvention to succeed long-term, publishers must continuously thwart newly added ad block filters and update their circumvention methods. However, it’s important to distinguish traditional ad-block circumvention from the latest ad-block recovery technology. To understand the differences, let’s take a closer look at how traditional ad block circumvention works, its limitations, and examine alternative ad block recovery strategies.

How does ad block circumvention work?

Ad blockers detect ads and block them from being displayed. Ad block circumvention is the process of detecting and re-inserting those blocked ads. There are various methods for ad blockers to detect ads, and circumvention is only effective when using a re-insertion method capable of countering the ad blocker’s initial "attack". The most common methods of traditional ad block circumvention are HTML/CSS obfuscation and server-side ad insertion (SSAI).

1. HTML/CSS obfuscation

Ad blockers often detect advertisements with an HTML/CSS filter. For example, filtering  would block ad elements with the class name ‘wing_banner’, and  would block ad elements with the id ‘banner_123’.

Publishers can circumvent those filters by obfuscating their ad’s HTML attributes (elements), such as the class name and ID. By doing so, ad blockers fail to detect the obfuscated ad as an ad unit, allowing the ad to bypass the blocker and be displayed to users.

2. Server-side ad insertion (SSAI)

Ad blockers can block advertisements, analytics, and tracker servers with network filters. For example, filtering [](<>) would block all outgoing traffic to Filtering* would block outgoing traffic to all /ads file paths, such as [](<>). By blocking all outgoing traffic, ad servers cannot communicate with clients, meaning ads cannot be displayed. As such, network filters are highly effective against client-side ad insertion (CSAI).

SSAI circumvents network filters by embedding ads directly into videos, bypassing the need for client-to-ad server communication. Because the content server relays content with the advertisement already stitched in, ad blockers cannot block the server without blocking the content as well. Dynamic ad insertion, a form of SSAI enabling ad customization, is particularly popular with video streaming services such as YouTube.


Though the above methods theoretically work under the right conditions, ad block circumvention technology vendors are no longer in business. As mentioned at the start of our post, ad blockers constantly - and most importantly, successfully - thwart traditional ad block circumvention. This is because ad blockers, typically operating as open-source, are fortified by millions of developers and users around the world. (AdBlock Plus, for example, has a running repository of filters dedicated to preventing ad block circumvention.) Ad blockers’ efficacy is to the extent that Facebook, the representative remaining utilizer of traditional circumvention, has an estimated recovery rate of just 20-30% (as per our research). Keep in mind that this is with Facebook’s massive engineering resources, including multiple teams dedicated to ad block circumvention. Though Facebook has the firepower to, at the very least, continue fighting against ad blockers, traditional ad block circumvention vendors lacked the necessary resources to maintain effective circumvention solutions.

Another major issue with traditional ad block circumvention is its incompatibility with script ads. For script ads to function, the proper execution of advertising scripts and communication with ad servers are required. Ad blockers easily filter both advertising scripts and ad servers, making it impossible for traditional circumvention to recover script ads. This limitation prevented traditional ad block circumvention vendors from working with major ad networks, including Google. Unable to monetize from ad networks, they attempted to generate revenue by circumventing and recovering advertisements for direct advertisers. However, because of limited demand, traditional ad block circumvention vendors were unable to operate sufficient CPMs and fill rates, leading to their business failures.

Alternatives and improvements

Thankfully, there are various alternatives to traditional ad block circumvention for revenue recovery. Commonly considered strategies include increasing ads, Acceptable Ads, ad block walls, and browser integrity recovery. Though each has pros and cons, they typically trade off short-term results vis-à-vis good UX. (For more information, check out our ultimate guide to ad block recovery strategies.) Of the alternatives, only Ad-Shield’s browser integrity recovery shows high returns and long-term results.

Ad-Shield’s browser integrity recovery, like traditional circumvention, detects and re-inserts blocked ads. But instead of depending on simple obfuscation or SSAI - neither of which are, as we examined, viable for long - solutions like Ad Shield’s Runtime leverage the technical limitations of ad blockers to implement an integrity-guaranteed layer on top of browsers. By executing advertising scripts on the secure additional layer, existing ads are successfully displayed to ad blocker users. Ad-Shield has mitigated over 4,000 ad blocker filter updates and consistently recovered over 90% of ad-blocked impressions. We understand the power and consequences of UX, so our technology recovers ads without bothering your users in any way. To learn more, reach out to our team of experts now for a free consultation.

Joon Yu
Founder & CEO