Apple will begin imposing new guidelines for iPhone, iPad, and iPod touch app developers starting on May 1 that require their apps to support Retina Displays. That restriction also includes a stipulation that iPhone apps must support the iPhone 5 and fifth generation iPod touch 4-inch screen size.
Apps that are already available on the App Store by May 1 can stay, but updates and new app submissions will need to include Retina Display support, which means the number of apps with blurry interfaces or black bars so they fit the iPhone 5 screen will start dropping off.
Developers must also stop using device UDID numbers to track users and instead need to "associate users with the Vendor or Advertising identifiers introduced in iOS 6."
Apple first started pushing developers away from UDID numbers in August 2011, and by March 2012 was rejecting some app submissions that relied on the identifier code to track users. Shortly thereafter, word surfaced that Apple had an alternative system in the works.
The company's decision to phase out UDID support was somewhat prescient because in September a group of hackers published a list of about a million user's ID codes they claimed they stole from an FBI laptop. The FBI denied they had a list of the codes, Apple denied giving the agency the codes, and in the end it turned out that the hackers stole the data from an app developer.
Developers that aren't already in compliance with Apple's new guidelines can check out the company's website for information on how to get up to date.