Apple’s recently released iOS 9 includes an update to WebKit, used by Safari and other applications that use the newly released SFSafariViewController, which enables a limited form of content blocking based on the URL and type. Its release has caused a significant impact - paid ad blockers now sit in the top of the paid app positions in the iOS app store, despite penetration of iOS 9 being at 25%. Update 21 September; it's now over 50% according to Apple.
The reaction to the ad blockers has been predictable for the most part. Websites that provide advertising along with their editorials are concerned that this will impact revenue; while users have reported significant gains in battery and network performance by blocking tracking scripts and sites. Some sites — such as CNet — have adjusted their video delivery to determine if a content blocker is being used and then flag up a warning, as reported by LoopInsight.
Christopher Soghoian of the ACLU observed that ad networks had an opportunity to work with the community previously with the introduction of the Do Not Track header, which was routinely ignored by web servers and advertising networks:
The most popular ad blockers: Peace, Purify and Crystal and 1Blocker, all shot up to the top of the paid app store charts shortly after release. However, in a surprising about-turn, Marco Arment pulled the Peace ad blocker, only days after its arrival. He said he didn’t feel good in profiting from the lack of advertising revenue from sites they visited. He subsequently explained that Apple has refunded all customers, despite this being unusual for Apple to do.
Safari’s ad blockers — more correctly called content blockers — are implemented in a way to be performant whilst also separating the blocking script from any visibility from the underlying page. These content blockers are loaded in a Safari extension, which sits in a different process from the web page rendering engine. The content blocker never sees the URLs that the user is requesting; rather, the blocker supplies a list of known bad (or good) sites and then lets Safari handle the filtering. The next version of OSX, due to be released at the end of September, also supports the same content blocking mechanism.
What, then, do the ad blocker applications actually do? Essentially they allow user editable block lists to be passed into Safari. Apple doesn’t make it possible to generate or edit this block list directly — they have to be supplied as part of a content extension — but ad blocking programs come either with a list of pre-installed filters (for blocking existing ad agencies or trackers) or allow the user to add their own by customising entries. There’s even a “Report this site” in some blockers which can be used to indicate to the author that there are more ad blocks required. Multiple content blockers can be installed and operational at the same time, and individually disabled on an application level through the Safari settings widget.
Where will this end? Sites need a way of monetising their content - including this one. Starting a content-blocking war by disabling parts of the site seems anti-user and may even impact the very users they are trying to keep. Meanwhile, the fact that targeted blocks are generally represented as a blacklist means that ad networks will likely keep changing domain names to evade hard-coded filter lists.
Ad blocking is not new, nor unique to mobile devices. However, the growth of web browsing on the mobile is easily the largest single demographic, and that doesn’t show any sign of slowing down. With iOS now supporting ad blockers (to improve battery and network performance, remember) and significant gains to be had on the browser side, it’s likely that many more non-technical users will start appreciating the benefits of using them. In the end, sites that rely on advertising as their main revenue source will have to find different ways of gaining revenue. Stratechery suggests that a new model of publishing is in order, because web pages suck. Whether the sites will suck more or suck less because of content blockers remains to be seen.