The new tool, which could be detailed in the coming weeks, aims to better protect user privacy than existing approaches, these people said. It comes after Apple last summer rattled the mobile industry by saying it would stop allowing app makers to use a unique identifier embedded in iPhones and iPads to track users across different apps. So far, the company hasn't aggressively enforced that policy.
The UDID or Unique Device Identifier is used by ad companies and developers to serve ads and get important usage data like location and preferences. Privacy advocates were concerned that the anonymous id could be coupled with enough data to identify an individual since it was tied to a specific device.
At this point in time it's unclear how Apple's solution would work; however, it's likely it will be detailed in depth at WWDC.