Testing Third Party Cookie Blocking

For the past few months Performics has sampled data from our tracking servers to measure cookie blocking rates. I have been running experiments using this data to nail down exactly when and why cookies are getting blocked. Last week, Peter discussed the story about an IAB study on third party cookie blocking. I was particularly interested because I was in the middle of an experiment that was initiated by some startling statistics from our own measurements. The numbers were quite interesting (and deserving of a separate post which I’ll be publishing soon), but even more interesting were the scenarios under which cookies were blocked due to being classified as “third-party.” Before I dive too deeply into this topic, it would be useful to review some relevant definitions of third party cookies.

Here is the description provided from Microsoft:

A third-party cookie either originates on or is sent to a Web site different from the one you are currently viewing. [1].

The definition used by the Mozilla group is similar, “Cookies that are stored by a site other than the one you are visiting are called third-party cookies or foreign cookies.” [2]

Using these definitions, cookies set by a tracking system are not considered third-party cookies provided the link is clicked directly and is the primary link in the browser. There are some methods of linking that affiliates employ that do result in a network cookie being regarded as third party (e.g. HTML frame, IFrame, image reference, etc.). The following experiment will illustrate my point:

1. Delete any cookie on your machine associated with the clickserve.cc-dt.com domain (in IE, the cookie will be named “link”, in Firefox you should be able to find it by the domain).

2. Instruct your browser to block third party cookies

a. In IE, Tools -> Options -> Privacy, override default settings, block third party cookies
b. In Firefox, open preferences, view the privacy tab, check “for the originating site only”

3. Point your browser at this page: http://lea.freeshell.org/revenews-example.html - the page has an IFrame that is a reference to the Performics tracking server.

4. Check for the cc-dt.com cookie. It should not be there. The IFrame is third party content since the page is hosted at lea.freeshell.org.

5. Now, click this link: http://clickserve.cc-dt.com/link/click?lid=41000000009104360 (This is a live link from Performics’ network associated with a test account used for troubleshooting so I’m not making any money off this in case you were wondering).

6. Go back and look for a cookie from cc-dt.com (in IE, the cookie is named “link”).

I’m willing to bet that it’s there. The first example attempts to set a cookie from a third party context, the second sets the cookie from the first party context. The user is in fact requesting to visit Performics’ server directly (cc-dt.com) prior to being redirected to the merchant site.

If you still do not see a cookie there are other reasons why it may not have been set. Your browser may have been manually configured to block the domain, or a privacy/anti-spyware program may be targeting the domain, a text pattern in the url or other marker. This is a different, and much less pervasive problem (I’m working on more accurately measuring this now).

In looking through the numbers, I did see an almost unbelievable variance in cookie blocking rate depending on the source of the traffic. The numbers ranged from less than one percent to more than seventy-five percent in a few extreme cases. Most often, the distinguishing factor between a site with a high rate and one with a low rate was that the low rate site had only direct links while the high rate site used frames, iframes or other attempts at setting the cookie upon a page view. I’m going to follow up with a post on this, too as there are some interesting implications to this phenomenon of site-level variance.

Affiliates, this means that if you are framing tracking links, using IFrames to stuff cookies, or employing some other view-based cookie setting scheme, it is very likely that a large percentage of your cookies are being blocked. Try linking directly to see if your conversion rates improve.

I have already worked with one affiliate to modify their linking methods and have seen a two to six times increase in conversion since the change. Powerful stuff. (If you haven’t already, you may want to reset your cookie settings, but if you don’t, I’m not going to lose any sleep over it.)

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