Why ad-blockers actually do affect affiliate tracking

I saw a discussion recently about whether affiliate tracking is affected by third-party ad-blockers like Ghostery, AdBlock Plus or uBlock.

The general consensus seemed to be that ad-blocking isn’t a big problem for affiliate tracking, particularly compared with browser-based privacy restrictions like Intelligent Tracking Prevention.

The thought process here is that ad-blockers work at a ‘content level’, blocking page elements from displaying, like intrusive ads, and do not block at a domain level in a way that might interrupt affiliate links.

Which is more impactful to Affiliate, ITP or third-party ad-blocking?

I’m surprised at the way the affiliate marketing industry has down-played the impact of third-party ad-blockers, in favour of dramatically up-weighting the impact of browser-based privacy controls like Safari’s ITP.

There is very little empirical evidence – at least in the public domain – to suggest ITP is a more significant issue for affiliate tracking than third party ad-blockers. And ad-blockers definitely DO interrupt affiliate tracking.

However, we shouldn’t overplay any of these ‘tracker protection’ issues. Less than 5% of total affiliate sales in the UK are likely to fall victim to an online privacy device of any kind – be it browser-based or third-party. But it’s misleading for the industry to claim ITP is the nadir of affiliate tracking, and third-party ad-blocking is merely a pin-prick in comparison.

Contrary to popular belief, simply switching on an ad-blocker in a browser, clicking on some affiliate links and watching them run unmolested to the advertiser’s website is not confirmation that all is well. But we also shouldn’t assume that every time an ad-blocker is switched on it is doing something nasty to our livelihoods. As is often the case with online tracking, there are few absolutes and much depends on the way affiliate tracking code is implemented on advertiser websites.

The evolution of ad-blocking

To understand how modern third-party ad-blockers work, particularly in Safari, it’s important to understand Safari’s Content Blocking. Apple introduced it to Safari in iOS 9 and OS X 10.11 (El Capitan). This is the function ad-blockers use to help them block ads in Safari.

Before content blocking came along, the rules ad-blockers used to determine what should be blocked on a page were executed using JavaScript and controlled exclusively by the owner of the ad-blocker. Safari’s Content blocking mechanism converts these rules to compiled code, which essentially means they are more inter-woven into the functionality of the browser, rather than purely an add-on.

This is important because it often means the work of a third-party ad-blocker is now done in the background without the user being aware of what, if any, ad-blocking is taking place. It’s also then easy to misinterpret if any online tracking disruption is the work of in-built browser privacy controls or a third-party.


How to view and control ad-blockers on a mac

Users can control their content blocker settings in Safari by going into Preferences > Websites and then reviewing the Content Blockers section:

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All ad-blockers in Safari are installed via extensions, which can be viewed in Preferences > Extensions.

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We ran some tests…

I use Safari 12.1 (the latest version at the time of writing) and I have Ghostery Lite and AdBlock installed.

I completed 5 affiliate-linked transactions with content blocking disabled. All 5 transactions tracked without incident to my cashback account.

I then switched on content blocking for all websites (this is the default setting for a user that has an ad-blocker installed). I also cleared any pre-existing cookies related to my previous transactions.

I made the same 5 transactions for the same advertisers. Two failed to track.

While I appreciate this isn’t a far-reaching test, it gives some indication that third-party ad-blockers are affecting affiliate tracking, and perhaps more than any native browser functionality.


Testing this yourself

Third-party ad-blockers use Safari’s content blocking framework to block a significant number of online trackers. Affiliate marketers can view the impact of content blocking in Safari pretty easily.

Go through the above steps to toggle content blocking on/off in Safari, and then click on an affiliate link to visit an advertiser’s website. Once the advertiser’s website has loaded, open the Developer console – Develop > Web Inspector > Storage (here are instructions on how to active the Developer Tools in Safari)

Expand the Cookies tab. Do this with content blocking on and off and notice the difference in the amount of third-party cookies that are loaded on the page:

Content Blocking Off:

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Content Blocking On:

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In this example, when content blocking through Ghostery Light was switched on we can see affiliate network, analytics and ad-serving cookies all being blocked.

However, this doesn’t mean we should have an ITP-style industry implosion. Yes, we’ve demonstrated that ad-blockers actually do block affiliate tracking. But for other advertisers affiliate tracking will be unaffected by the very same ad-blocker. Try it for yourself. It’s situation which highlights the need for affiliate marketing to stop thinking that ad-blocking and/or browser privacy restrictions operate in a binary or consistent way.


Moving forward in a rational way

Ad-blocking is an issue for affiliate marketing, no lesser or more significant than issues such as Intelligent Tracking Prevention. The way third-party ad-blocking affects affiliate tracking is a reminder to the industry of two key things that have to happen if the accuracy and reliability of affiliate tracking is to improve:

  1. Avoid the use of third-party container tags when implementing affiliate network tracking of web-based tags for publisher

  2. Affiliate tracking should be implemented sever-side to avoid relying on web requests to record clicks and conversions