With the stepped up talk from Congress about security, Apple has announced that they are killing access to UDiDs by apps.
Each and every iPhone and iPad has a UDiD, or Unique Device Identifier, an alphanumeric number unique to a device. Currently this information is being used by mobile advertising networks, game networks, analytics providers, developers and app testing systems. Specifically, mobile advertising networks use the UDiDs to tailor advertising to the user. With this information now no longer available, these networks are going to have to find other ways of making sure their adverts reach the right people.
However, there are real privacy risks attached to these numbers. They can't be cleared or deleted like cookies on the internet. So with Congress investigating privacy concerns and pressure from the media, Apple jumped before they were pushed.
Apparently, Apple had warned some of the larger mobile-social developers that this news would be coming soon, and advised them to begin to find alternatives to the information provided by UDiDs. It was also stated in some iOS documentation almost six months ago. Since that warning, Apple is now simply rejecting apps that require access to UDiDs.