Apple will officially start rejecting iOS apps that make use of the unique device ID or UDID, in order to track users. The company informed its developer community of the policy late Thursday (followed by a confirmation to Macworld) that it would no longer accept UDID-utilizing apps as of May 1. Instead, the company instructed developers to make use of other identifiers, such as Apple's new Identifier for Advertising, or IDFA, which was introduced in iOS 6 last fall.

Apple had already warned developers in early last year that it would begin deprecating the UDID, and it had been rejecting apps that make use of it as early as May 2012. That didn't stop every developer from using the UDID, though, and a high-profile leak in September (originally suspected to have come from the FBI but ultimately revealed to have come from an iOS app publisher) highlighted the need for a more privacy-conscious system to track users and offer targeted advertising.

That's part of why Apple introduced its IDFA when it rolled out iOS 6. Not only do users have more control over whether they are being tracked; the IDFA also allows developers to follow iOS users across devices. With the UDID, users had no way to turn off the ad tracking, and since the UDID was tied to a specific device, the data could be cross-contaminated if a new user took control of it.

The no-UDID policy isn't the only thing Apple announced this week. The company also told developers that as of May 1, it will no longer accept apps that have not been adapted to the iPhone 5's taller 4-inch screen, or those that don't support retina displays.