Apple has begun rejecting apps that use software development kits (SDKs) that engage in fingerprinting.

Fingerprinting is a method of collecting data and tracking users, creating a unique device fingerprint that can be tracked across services. As part of iOS 14’s improved privacy, Apple is now rejecting app submissions that use SDKs known to engage in this behavior.

According to AppleInsider, a number of developers have already been notified of rejections.

“Our app just got rejected by Apple’s app reviewer, blaming the MMP SDK for building a fingerprint ID,” wrote Heetch‘s Aude Boscher, in an industry Slack channel. “I saw other people complaining … so it might soon come up for you as well!”

Apple’s notification message clearly says what the problem is:

Your app uses algorithmically converted device and usage data to create a unique identifier in order to track the user. The device information collected by your app may include some of the following: NSLocaleAlternateQuotationBeginDelimiterKey, NSTimeZone, NSLocaleGroupingSeparator, NSLocaleDecimalSeparator …

Adjust makes one of the offending SDKs, used by some 50,000 apps. The company has released an update that removes the offending code, however, providing a path forward for the apps using it.

While the change is no doubt inconvenient for developers, kudos to Apple for cracking down on one of the more insidious methods of tracking users.