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Who blocks the (ad) blockers?

With <i>The New York Times</i> picking up the recent story of the (mostly minor) anti-Adblock Plus protest, its worth looking into the subject and seeing just where a Webmaster/ad-block developer arms race could take us.

Chris Soghoian
Christopher Soghoian delves into the areas of security, privacy, technology policy and cyber-law. He is a student fellow at Harvard University's Berkman Center for Internet and Society , and is a PhD candidate at Indiana University's School of Informatics. His academic work and contact information can be found by visiting www.dubfire.net/chris/.
Chris Soghoian
4 min read

The New York Times recently covered the already over-hyped dispute between Danny Carlton, an obscure Web site designer, and the makers of the popular Adblock Plus Firefox browser extension.

Adblock Plus is something akin to a TiVo for Web-browsing. Users who install the extension will find that their Web experience is radically changed--in that the vast majority of graphical Web advertisements will no longer be displayed within the Web-pages that they visit.

For those of you with short memories, it's worth noting that before TiVo was the only major game in town, there used to be another TV advertisement skipping technology. ReplayTV was vastly superior to the TiVo, in that it completely skipped commercials, instead of permitting users to fast-forward. Following a similar tactic to that was used by the major media companies (who had previously gone after Napster and the VCR), the TV networks essentially sued ReplayTV out of existence. The moral of the story: companies that have built their business models on advertising revenue do not take kindly to others who permit customers to skip those advertisements.

With that little walk down memory lane over, let us focus on the issue at hand--Web advertisement skipping technology. Essentially, it boils down to this: Web site designers depend upon advertising revenue to pay their bandwidth bills as well as to pay for the staff time that goes into making a successful site. Users do not particularly want to see advertisements, but except in a few cases where advertisements are extremely annoying, will for the most part put up with the ads in order to view the Web content that they are seeking.

There is a pretty big difference between the TV and Web site business models. A broadcast TV network, by and large, has fixed costs, no matter how many customers actually tune into the show. The same amount of electricity will flow to the TV transmitter, and the satellites above will still beam down the same number of 1s and 0s. Internet content is different, as each person's computer makes an individual connection to the remote server hosting whatever Web content the user is seeking. Each time users visit a Web site, the server consumes bandwidth to send the content of the Web page back to the user--and that bandwidth costs money.

Thus, every time someone uses advertisement-blocking software to avoid the graphical ads embedded within a Web site, they are denying the Web site operator revenue that would otherwise have gone to pay for the bandwidth that is consumed during that browsing session. While it could be said that TiVo users are freeloading from the broadcast networks, users of Web advertising skipping technology are far closer to theft than they are to freeloading. This is not a clearly defined issue, but there are a significant number of moral issues at play.

Which now brings us to the technical issues involved in this particular story...

The person running the anti-Adblock Plus campaign has been unable to remotely detect which Web surfers visiting his site have installed the extension, and so, in an effort to pressure both the developers of Adblock Plus and the Firefox browser development team, has instead called for Webmasters to completely block the Firefox browser. Call it collateral damage, if you will.

It turns out that Danny Carlton, the man behind the boycott, is using an implementation difference in the document.all() Javascript function to determine which users are visiting his site with Firefox and which are browsing with Internet Explorer. For those of you Firefox users desperate to view his Web site, a highly effective technique which will allow you to evade his simplistic browser detection technique is to lie about your browser's User Agent and turn off Javascript. While this can be done within the Firefox preferences, an even better method is to download and install the User Agent Switcher and NoScript Firefox extensions. In particular, NoScript is a must-have Firefox addition which will allow you to create a Javascript blacklist for individual Web sites.

If Danny wishes to block Firefox users who have turned Javascript off, he could use implementation differences in Cascading Style Sheets (CSS). Furthermore, due to a trick discovered by uber Web-application security hacker RSnake, it is possible for Web site designers to figure out exactly which Firefox extensions you are running. This was first reported to the Firefox development team in 2005, but has yet to be fixed. The developers of Adblock Plus have developed and deployed their own fix to this problem, but most other extensions are still vulnerable. If they wished to, Google could quite easily use this bug to to blacklist users of the Customize Google Firefox extension, which among other things, allows users to block Google's text advertisements.

In the end, a few things are clear: Users of advertisement-skipping technology are essentially engaged in theft of resources. Web site owners have not, yet, wrapped their Web sites in shrinkwrap contracts, and so while the ad-skipping may be immoral, it certainly isn't illegal. Web site owners are perfectly within their rights to utilize any and all browser/extension/Web behavior detection technologies in order to blacklist the ad blockers. Similarly, creative users are more than within their rights to evade whatever detection technology the Web site designers use.

The real question to be answered is: will other Web site owners wish to get themselves into an arms race that they almost certainly cannot win?