Ad-blocking History, Impacts, Techniques and Countermeasures

Part 2: Impact of Ad-Blocking

To gain insight into just how big of an issue ad-blocking is, I recently crunched all of my server logs for for the last six months of 2005. I cross referenced the number of daily unique visitors I got against the number of visitors I rerouted to my banner blocking page. I also cross referenced the daily page views reported by my server logs against my Google AdSense stats.

As a point of reference, the stats program I use is AWStats and it has been configured to detect around 400 known robots and automated processes, however I am unable to detect robots that cloak themselves by reporting the UA strings of normal web browsers. Although this browser spoofing will affect the stats I believe the impact is very nominal.

Due to the way I implemented ad-blocking countermeasures on my site, it is only possible to provide a high and low limit as to the percentage of users who are blocking ads not an exact estimate. The low limit was calculated by comparing the total number of visits per month against the number of visits that resulted in the user being redirected to my banner blocking page. Because some ad-blocking methods prevent JavaScripts from running or prevent the JavaScript "onload" event from running correctly, not all users who block ads get redirected to this page. The high limit was calculated by comparing the number of page views that should have displayed a specific Google AdSense ad with the actual number of AdSense ads that were displayed.

Month % of Visits Blocked Due to Ad-Blocking % of Page Views Where AdSense Ads Did Not Load
Jun-05 3.54% 12.32%
Jul-05 3.31% 11.97%
Aug-05 3.75% 9.89%
Sep-05 3.39% 9.15%
Oct-05 2.54% 10.94%
Nov-05 3.46% 9.74%
Dec-05 4.40% 10.35%

When I crunched my logs one figure I wanted to see if I could get a grasp on was what percentage of ad-blocking was due to which browser. The real problem with this is that due to the way logs were processed it is not yet possible to breakdown what percentage of users of a specific browser are blocking ads. It was only possible to show the relative percentage of banner blocking for specific browsers. For instance, in June 2005 Firefox accounted for 25.4% of traffic that was blocking ads. More specifically in June 2005 Firefox accounted for 25.4% of requests for the file "/banblock.html", which is only requested when the user gets redirected because they are blocking ads.

If the percentage of total traffic for a specific browser is lower than the percentage of banner blocking traffic for that browser then users of that browser are blocking ads more frequently than users of other browsers. If the percentage of total traffic for a specific browser is higher than the percentage of banner blocking traffic for that browser then users of that browser tend to block ads less frequently than other users.

For example, Firefox users consistently block ads more frequently than MSIE users. In part this is because of the Adblock extension that users can download for Firefox. One obvious omission from the following list of browser stats is the Opera web browser. Opera was omitted because it consistently generates less than 0.3% of the total traffic for making any analysis of it statistically irrelevant. One very interesting trend that is disclosed by the table below is that the relative percentage of users blocking ads compared to other users (MSIE users in particular) has been steadily dropping over the past six months even though the total percentage of users using Firefox has climbed modestly over the same period. Why this is happening is anybody's guess.

Month Browser % of Total Traffic % of Banner Blocking Traffic
Jun-05 Firefox7.6% 25.4%
Jun-05 Mozilla 1.5% 1.4%
Jun-05 MSIE 87.4% 68.9%
Jun-05 Netscape 1.3% 1.3%
Jun-05 Safari 1.3% 1.1%
Jul-05 Firefox 8.3% 21.8%
Jul-05 Mozilla 1.6% 1.1%
Jul-05 MSIE 86.5% 73.8%
Jul-05 Netscape 1.4% 1.5%
Jul-05 Safari 1.4% 1.2%
Aug-05 Firefox 8.2% 23.5%
Aug-05 Mozilla 1.4% 1.9%
Aug-05 MSIE 87.3% 71.9%
Aug-05 Netscape 1.2% 1.3%
Aug-05 Safari 1.3% 0.8%
Sep-05 Firefox 8.1% 14.7%
Sep-05 Mozilla 0.9% 0.8%
Sep-05 MSIE 88.0% 81.7%
Sep-05 Netscape 0.9% 1.2%
Sep-05 Safari 1.5% 0.3%
Oct-05 Firefox 7.6% 21.7%
Oct-05 Mozilla 0.7% 3.1%
Oct-05 MSIE 88.4% 72.0%
Oct-05 Netscape 0.9% 1.2%
Oct-05 Safari 1.6% 0.0%
Nov-05 Firefox 7.5% 16.2%
Nov-05 Mozilla 0.7% 1.0%
Nov-05 MSIE 88.2% 79.0%
Nov-05 Netscape 0.9% 1.2%
Nov-05 Safari 2.0% 1.3%
Dec-05 Firefox 8.2% 16.4%
Dec-05 Mozilla 0.9% 0.8%
Dec-05 MSIE 87.0% 79.8%
Dec-05 Netscape 0.8% 0.6%
Dec-05 Safari 2.1% 1.1%

While there is obviously great room for discussion as to what percentage of users are blocking ads and that percentage changes depending upon the demographics of the site in question, it is fairly obvious that ad-blocking is having a real economic impact on websites.