"So I've heard you've been breaking some of our rules," was how a meeting began between Tim Cook and Travis Kalanick in early 2015, according to the New York Times. Uber had been tracking iPhone users after uninstalls, and until that point, evading Apple's attention.
The New York Times report tells a story of Uber CEO Travis Kalanick going to Apple's headquarters for a meeting with Tim Cook, in which he was calmly chided by the Apple CEO and told to start following the rules or have his app pulled from the App Store. Uber was apparently tracking iPhones after the app had been uninstalled. It had disabled the functionality in the vicinity of Apple's headquarters in an attempt to fool its Cupertino engineers, but testers in other locations picked up on the activity.
The technique is called "fingerprinting", which identifies a device and remains even after it's wiped. Apple had previously given developers the ability to mark devices with a Unique Device Identifier, which new installs wouldn't get rid of, but eventually scrapped the technique in favour of more privacy-prudent protections. Uber's fingerprinting, however, was one of its own design.
Regarding the fingerprinting, an Uber spokesperson told the following to TechCrunch:
We absolutely do not track individual users or their location if they’ve deleted the app. As the New York Times story notes towards the very end, this is a typical way to prevent fraudsters from loading Uber onto a stolen phone, putting in a stolen credit card, taking an expensive ride and then wiping the phone—over and over again. Similar techniques are also used for detecting and blocking suspicious logins to protect our users’ accounts. Being able to recognize known bad actors when they try to get back onto our network is an important security measure for both Uber and our users.