Enlarge / Social media applications are seen on an iPhone in this photo illustration in Warsaw, Poland on December 17, 2020. Facebook has disabled several features on it's Messenger app to comply with new data usage rules currently being put in place in the EU as aprt of the ePrivacy Directive. (Photo illustration by Jaap Arriens/NurPhoto via Getty Images) (credit: Getty Images)

App developers are exploring surreptitious new forms of user tracking to evade Apple’s new privacy rules, which threaten to upend the mobile advertising industry in the coming months.

Early in 2021, an iPhone update will prevent apps from using advertising identifiers known as IDFA without obtaining each user’s explicit consent for targeting. Developers expect more than two-thirds of users will block tracking when they see a pop-up appear within their apps.

Some app makers say they plan to use invasive tracking techniques such as “device fingerprinting” to work around the new restrictions—even though doing so risks getting them thrown off the App Store if they are caught.