Apple has announced that it will start rejecting apps that aren't Retina-ready, compatible with Apple's 4in iPhone display, or use UDIDs from 1 May.

Apple alerted developers with the following post: "Starting May 1, new apps and app updates submitted to the App Store must be built for iOS devices with Retina display and iPhone apps must also support the 4-inch display on iPhone 5."

This means that if a developer wants to fix any bugs or add new features to their iPhone apps they will have to make sure that the app fits the iPhone 5 screen and meets the requirements of the Retina display.

The Next Web suggests that the side effect of this is that the new screen size requirements mean that new updates will not support iOS 4.2 devices as they need to be built with the iOS 6 SDK, which includes features that aren't compatible with older versions of the software. This could make some iPhones and iPod touches obsolete. 

UDIDs and privacy

With regard to UDIDs, Apple stated: "Starting May 1, the App Store will no longer accept new apps or app updates that access UDIDs. Please update your apps and servers to associate users with the Vendor or Advertising identifiers introduced in iOS 6."

Apple had already eliminated Universal Device IDs (UDID) and replaced it with a new Limit Ad Tracking feature in iOS 6. When users enable the feature, they are basically letting mobile applications know that they do not want to be tracked. All applications that run on iOS 6 need to check the setting first before attempting to collect any kind of tracking data. If the limit tracking feature is enabled, advertisers and online ad network will only be allowed to collect only a narrow set of data related issues such as security, debugging and keeping a tally of unique users.

To Limit Ad Tracking on your device: Settings > General > About; Scroll down to Advertising; Flip 'Limit Ad Tracking' to ON.

UDIDs attracted attention last year when a hacker collective known as AntiSec published over a million Apple device IDs that it claimed were captured from the laptop of an FBI agent. It turned out not to be the FBI, but an app development company called BlueToad who acknowledged that its database of Apple iPhone, iPad and iPod Touch unique device identification (UDID) numbers was breached.

Apple's UDIDs are basically a set of alphanumeric characters that are used to uniquely identify an iPhone or iPad. The numbers are designed to let application developers track how many users have downloaded their application and to gather other information for data analytics.

In 2010, The Wall Street Journal did an investigative report showing how application developers were using Apple's UDID to gather a lot of personal information about the device owner, including name, age, gender, device location and phone numbers. In response to concerns about the tracking, Apple earlier this year stopped allowing new iOS applications to track UDIDs.

Even before the breach, Apple was warning developers against using UDIDs. started banning apps that used them. Last April we reported that the rejection of several new apps using UDID data from the App Store has lead to concerns that Apple will block iOS apps that use UDID (unique device identifier data).

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