The issue of the reliability of cookie-based tracking is perhaps one of the most important issues for affiliates and always has been.

Affiliate marketing operates on the basic assumption that the sales affiliates refer to advertisers are tracked and reported correctly.

It is helpful to think of two separate but linked aspects to the issue of reliability. Firstly, there are the technical aspects around the reliability of cookie-based tracking: what technologies are available and how reliable are they?

Second, there are user-based or privacy issues. These are related to technical issues but concern more precisely users’ understanding of how cookies are used and their possible motives for deleting them.

The technological reliability of cookie-based tracking in and of itself is pretty robust. Where technical problems in tracking occur they are far more likely due to a failure of the tracking on the advertiser’s site firing than to the cookie placed at the time of the user’s click.

In terms of the user-related aspects things are more complicated. Recent research by Specific Media indicates that the public attitude to the use of cookies is fairly relaxed. Users understand cookies are necessary to store preferences and details, and are comfortable that they are used to serve ads.

There is more concern around behavioural retargeting though, echoed at a supra-national level in the form of the EU’s ePrivacy Directive, something which will affect advertisers, affiliates and networks alike, and is therefore almost certainly the biggest industry-wide challenge that affiliate marketing currently faces.

Examining in more detail how these dual aspects, technical and user-based, interact, it is helpful to distinguish between different types of cookies and look at their respective likelihoods of deletion.

Affiliate Window uses first party cookies set by the domain and so are likely to suffer lower deletion rates than third party cookies set by third parties. The vulnerability of third party cookies varies by browser.

Safari automatically blocks third party cookies, as will certain plugins for other browsers, which could pose a problem for advertisers relying too heavily on certain third-party tracking solutions.

Web monitoring firm comScore has analysed cookie deletion patterns and in April 2010 reported that third party cookies were deleted by 30-40% of users and first party cookies were deleted at rates in excess of 20% (source).

This data however is not specific to the affiliate channel and it is likely that users find certain other methods of cookie-based tracking more invasive and thus delete them.

In response to the implementation of the EU’s ePrivacy Directive behavioural re-targeters have implemented a button displayed in their ads which directs to a site offering users more information and the ability to opt-out. It is possible that UK affiliate marketers might have similar recourse in the near future.

However, opting out and cookie deletion are two separate things. Opting out does not bear on the reliability of tracking methods in and of themselves; indeed, a persistent cookie has to be set on a user’s machine in order for an opt-out preference to be stored!

So what alternatives are available?

An affiliate network should offer additional tracking methods for redundancy that can help reassure affiliates worried about high deletion rates. IP-based tracking, ETags and Flash cookies are some examples (more about these here) but on Affiliate Window these are necessary in only a small minority of cases.

Flash cookies have the advantage of tracking across different browsers (if a customer shops in IE but buys in Firefox, for example) and are stored separately to other cookies. Because the user has to go through a different process to remove these they are also less likely to be deleted.

Affiliates that work on dual-network campaigns and have switched from one to the other have sometimes reported a mysterious change in the volume of sales they are producing. This might be an indication of the robustness of the different affiliate networks’ tracking methods.

It has also been suggested that cookie deletion might be encouraged by some affiliates (notably, cashback sites) in order to minimise members’ transaction queries.

However, it is worth pointing out that at present neither of the two largest cashback sites prompt their users to delete cookies prior to clicking through to an advertiser, and do not appear to offer information on how to delete other affiliates’ cookies.

In conclusion, whilst the technological aspects of cookie-based tracking remain sound, in the current political climate following the adoption of the EU’s ePrivacy Directive the issue of how cookies are used is creeping closer to the forefront of public consciousness.

As the affiliate industry like others adopts different methodologies to track and attribute sales transparency to users will be key in determining whether we witness a rise in opt-out and deletion rates.

Owen Hewitson

Published 8 November, 2011 by Owen Hewitson

Owen Hewitson is Client Strategist at Affiliate Window and a contributor to Econsultancy.

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Comments (11)

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I think it's particularly interesting that some affiliates have noted a significant uplift in sales volumes when they switch networks - can't argue with evidence like that! I'm also quite surprised at the figures quoted on the number of people who delete cookies. Much higher than I would have estimated. Thanks Owen, will be bookmarking this article.

almost 7 years ago

Peter O'Neill

Peter O'Neill, Founder & Lead Consultant at L3 Analytics

Hi Owen,

A big factor impacting on the accuracy of cookie based tracking is multiple device use. Many people use a work and home computer, let alone smart phone, iPad, etc. So even without cookie deletion, one person can appear as multiple unique visitors (one per device) in any web analytics or ad tracking tool.



almost 7 years ago


The Same Anonymous

Specific Media's 'research' was utter PR rubbish. Public attitude to cookies is not relaxed as perfectly illustrated by the deletion rates.

Secondly, if a user deletes a cookie it's because they don't want to be tracked. Suggesting that alternative tracking methods is therefore a 'backup' just illustrates how little regard for privacy ad and affiliate networks actually have.

Bring on tough legislation and sooner the better.

almost 7 years ago


Kevin Edwards

@The Sam Anonymous, you seem to have overlooked the primary audience of this site.

That aside, I think the fact that the ICO has received a grand total of two complaints concerned with online privacy since the revised Directive came into law since May (albeit unenforced until next year), suggests it may be lower down people's list of priorities than you suggest it may be.

almost 7 years ago

Lee Cash

Lee Cash, Senior Business Development Manager at Qubit

@The Same Anonymous. Why do you think users are deleting cookies? Is it because they don't want the online marketing industry to support high quality content and user experiences through more effective tracking, relevancy and appropriately allocated marketing revenues? Or perhaps it's because the EU recklessly approached this issue, put together legislation that no one knew how to implement and then allowed the usual plethora of PR and journalistic scaremongers to get to work?

almost 7 years ago


The Same Anonymous

Kevin, you seem to have overlooked the point.

The primary audience of this site have a responsibility to understand that what they are doing will eventually lead to legislation which will damage the industry itself.

Consumers/users are concerned. The fact that they are not complaining is simply because they don't understand the extent of the tracking. Unfortunately, loss of privacy is a one way process (thanks to 'backups') and once users do realise, it'll be too late to get it back.

Antivirus companies have made good money from selling software targeted at blocking tracking. Browser manufacturers have launched browser versions on the back of cookie blocking and privacy features. This isn't random marketing. These features sell because users ARE concerned about tracking, cookies and privacy.

I cannot see how on one hand people in this industry feel the need to jump up and down about EU legislation and on the other seem to think it's OK to create tracking 'backups'. Essentially saying that a user's desire to remain private isn't their decision.

The bottom line is that tracking and invasion of privacy will continue until legislation stops it because this industry is incapable and unwilling to regulate itself.

almost 7 years ago


The Same Anonymous

You are journalists ?

Shame on you.

almost 7 years ago

Brian Clifton

Brian Clifton, Author, CEO & Web Metrics Strategist at Advanced Web Metrics

Owen: a very LARGE assumption is made in your article - that visitors use the same device. This is no longer valid and increasingly so - as pointed out by @Peter O'Neil. In my experience multiple device usage is a bigger problem than the issue of cookie loss.

@Lee Brignell-Cash quote:
"Is it because they don't want the online marketing industry to support high quality content and user experiences through more effective tracking, relevancy and appropriately allocated marketing revenues?"

Sorry Lee - I just *do not* see that at all. Visitors don't want to be tracked because they don't want their personal information picked up and spread around the web to 3rd-party companies they know nothing about.

There are of course tracking tools that explicitly do not allow this - GA for example. The problem is that poor (i.e. non-existent) regulation in this area over the years has resulted in the legislators coming in heavy handed. I don't blame them - in fact I support it, it just needs tightening up to allow benign tools to operate freely.

- Thoughts and comments on the EU Privacy Law:

- My whitepaper on web analytics accuracy (detailed and vendor agnostic):

Brian Clifton
Author, Advanced Web Metrics with Google Analytics

almost 7 years ago

Phil Pearce

Phil Pearce, Senior Web Analyst at Accelerate Agency Ltd


I understand you desire to increase affiliate conversion rates, by improving tracking accuracy.

If cookie blocking becomes a problem, then the blended CPA for all affiliates will just increase relative to the number of tracked sales.

Fore example:
+10% increase in CPA to account for a
-10% decrease in tracked affiliate sales.
Market dynamics should prevail

A word of a Caution: It is a very bad idea to recommend storing affiliateID`s within Etags, FlashCookie or HTML5 storage - until such time as the browsers update its privacy control panels; so that the same controls that exist for text based cookies, also exist for their etag/flash/html5 conter-parts.

Vendors and brands such as Kissmetrics and QuantCast, Hulu, Disney and others tried using theses techniques and they "got-burnt" by million dollar class-actions settlements and negative PR.

It is important to remember, that if the user has expressed the "intent" not be tracked then their permission should NOT be bypassed, or thier sessionID should NOT be respawned!

Ideally, you should:
* notify the user that they are being tracked
* tell them "why" they are being tracked
* and provide an opt-out or user-choice.

This choice becomes more important, if sensitive personal data (such as DoB, or postcode) is being tracked. Or if the data is being passed to a third party, such as a lead broker.

Instead of Etags, FlashCookie or HTML5 storage. I would recommend adopting the "ValueExchange" approach, by incentivise users to be tracked, and being open and honest.

* Tell them why it matters to them (i.e CashBack website could not exist without user-level cross-domain affiliate tracking, as their would be no way to share the revenue back to the user).

* Consider using Server-side device signatures from the logs of the affiliate and the brand owner - as this means that no cookie is set on the users machine, thus no consent needs to be gained. Obviously, a third party intermediary log processing engine is needed to remove PII & credit card data (such as HitWise/Tealeaf), but this is a safe solution, which is not too-blackhat, and it wont be effected by cookie deletion rates.

* Also, note that the ICO is currently reviewing HOW the Cookie legislation is to be implemented. Thus please don’t let the a handful of isolated incidents & recommendations within the affiliate industry - cause the whole "web analytics" sector to be marked as bad cookies...

It`s best to act in the best interest of the "user", atleast until May-2012 is over

Hope that helps


P.S there is a UK round table on Cookie Law at emetrics in a few weeks time:

P.P.S Here is a link to the self regulatory WA code of ethics and the self regulatory opt-out for cross-domain behaviural tracking for banner tracking:

almost 7 years ago


Kevin Barnes

I think the last comment sums up a lot of things. "customers don't want their information picked up and spread around". Their information is largely an anonymous IP address- and this is what people don't understand. They think their bank details, home address and times they're out during the day are all out there for Daily Mail inspired cyber criminals to pick up freely. The lack of understanding and why we collect it is the biggest issue, and I don't know how we get over that because people just don't have time to digest it and understand it.

almost 7 years ago

Brian Clifton

Brian Clifton, Author, CEO & Web Metrics Strategist at Advanced Web Metrics

@Phil Pearce - good points

Just a clarification - The Privacy session at eMetrics is about tracking privacy per se, not just cookies or the EU law, though I am sure those will be prominent ;)

almost 7 years ago

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