Harry Brignull is a London, UK-based independent user experience designer with a PhD in cognitive science. He is also the founder of Dark Patterns, which is dedicated to, in his words, "naming and shaming websites that use deceptive user interfaces." This article is based on a presentation he gave at the Search Marketing Expo in Munich this past April.

When Apple released iOS 6, one of the few new features not enthusiastically promoted by the company was Identifier for Advertisers (IDFA) ad tracking. It assigned each device a unique identifier used to track browsing activity, information advertisers used to target ads. Even though IDFA is anonymous, it's still unsettling to people who worry about privacy.

Fortunately, Apple included a way to disable the feature. You won't find it in the privacy settings, however. Instead, you have to go through a series of obscure options in the general settings menu. Now, "General” is a crappy name for a menu item. It’s mainly a bucket of miscellaneous stuff that they didn’t know what to do with. In the "General" menu, select "About." Down at the bottom of this menu, next to the terms of service and license items, there's a menu item listed as "Advertising."

If you haven't been here before, the only option in the advertising menu, "Limit Ad Tracking" is probably selected "Off."

But let's take a closer look at the way this is worded. It doesn’t say “Ad Tracking – Off” it says “Limit Ad Tracking – Off”. So it’s a double negative. It’s not being limited, so when this switch is off, ad tracking is actually on.

Off means on!

This is actually a great example of what I define as a "dark pattern."