• by Wendy Davis  @wendyndavis, June 12, 2013

Apple's newest version of its operating system for mobile devices, unveiled this week, contains new features that could make it harder for ad networks to track consumers.

The privacy features affect app developers that use ad-targeting technology other than Apple's own Advertising Identifier -- a tracking mechanism rolled out last year that lets consumers limit ad targeting.

Among other changes, Apple's iOS 7 restricts developers' ability to track people using Media Access Control addresses, which are permanent identifiers assigned to any device that's capable of connecting to the Web. As of Tuesday, app developers trying to access a MAC address are shown the identical number for all iOS 7 devices, according to Craig Palli, vice president of the mobile app platform Fiksu.

Until recently, many app developers and ad networks that tracked iPhone or iPad users did so using their devices' unique device identifiers -- 40-character alphanumeric strings, comparable to serial numbers. Studies in 2010 and 2011 showed that many of the most popular apps used the unique device identifiers to track iPhone and iPad users.

Two years ago, Apple said it would prase out developers' access to the unique device identifiers. But that move spurred some companies to turn to other tracking technologies, including MAC addresses.

A separate workaround used by app developers and ad networks involved pasteboards, or online clipboards. Apps would store data about devices on a pasteboard, which could be accessed by other app developers. But Apple's latest operating system also limits this ability, according to computer researcher and privacy advocate Jonathan Mayer.

“Until iOS 7, any app could access any clipboard data from any app (if it knew where to look),” Mayer says. “This is the hack they were using to get around deprecation of [unique device identifers]. That hack will be closed with iOS7, because only affiliated apps can see each other's pasteboard.”