Apple has begun rejecting iOS apps that access the device's UDID, which is the unique identification number that is attached to every iPhone and iPad, supposedly due to privacy scrutiny from Congress.
While the move was telegraphed by Apple in iOS documentation over half a year ago, these reported rejections are ahead of schedule and the first confirmation that Apple is indeed rejecting apps outright for using UDIDs. According to TechCrunch, two of Apple's ten app review teams have started rejecting all apps that access UDIDs as of last week. Two more teams will start rejecting apps this week, and keep escalating until all 10 teams are rejecting these apps.
The UDID was a privacy concern because it is permanently linked to the specific iPhone or iPad device, and security researchers discovered that some apps were transmitting user data out to remote servers, with real names in plain-text attached to the UDID. Even without specific information like a user's name or contact information, the UDID could identify a user with collected data.
Aside from the privacy concerns, Apple's rejection of apps that access UDIDs is a major issue for another reason: Advertising networks use the UDID to track data and improve advertisements, so a whole industry and a whole lot of money is tied into accessing this information. Without it, the ad agencies would have to figure out new ways to track data and statistics for their purposes. This could also have an impact upon app developers, who may have to spend significant amounts of time and resources to remove UDID access to update pre-existing apps.