Since the release of iOS 6.0 last fall, Apple has gradually begun changing the rules for in-app advertising and device identification, transitioning developers to a new “Advertising Identifier” in place of the older, permanent Universal Device Identifier (UDID). iOS 6.0 introduced the ability for users to opt out of this new form of tracking entirely via a rather obscure option tucked away at the bottom of the About screen in the Settings app.
With iOS 6.1, users now have an additional option that can be found here—Reset Advertising Identifier—that can be used to generate a new, unique Advertising Identifier for your device. This can be useful for those users who may not mind targeted ads or other forms of device tracking but may wish to effectively “start over” with a new unique advertising ID.
Apple includes a “Learn More” link at the bottom to provide more information on this feature, explaining that advertising networks are not yet required to use the new iOS 6 Advertising Identifier feature, and hence the use of the word “Limit” rather than “Disable” or “Opt-out,” suggesting that it will not yet completely eliminate ad tracking, but it’s definitely a step in the right direction if you’re concerned about this. Apple has begun transitioning developers away from using the UDID, and is expected to prevent third-party access to it entirely at some point, requiring developers to use the new user-controlled Advertising Identifier if they still wish to identify specific devices in their apps.