Apple's bulked-up Limit Ad Tracking feature is proving to be a hit among consumers.
Limit Ad Tracking, or LAT, is a setting on iOS devices that lets users prevent in-app ads from being targeted at them directly.
About 18 million iPhone and iPad users in the U.S., roughly 20% of the total, have used LAT to explicitly opt out of targeted advertising, according to a report released Wednesday by app marketing platform Adjust.
LAT has been available since 2012, but Apple strengthened it in the latest version of its iOS operating system by letting consumers completely avoid a unique ID number called the "Identifier for Advertising," or IDFA, rather than just resetting it.
"IDFA is Apple's highly accurate and privacy-sensitive device identifier," said Ben Roodman, AppsFlyer director of partner development, North America, in an email. "Basically, it's a combination of numbers and letters that is unique to each iOS device. IDFAs are commonly used by ad networks, retargeting providers, and other media sources to serve targeted ads and re-engage users on specific devices."
Users that enable LAT now become ghosts, the numbers that previously identified them left blank.
The update to LAT makes tracking behavior of iOS users significantly more complicated. It also affects ad networks like Google and Facebook, as well as marketers.
Global adoption rates of LAT have remained steady at around 18%, according to the report by Adjust. In the U.S., however, 2 million additional people activated the setting in September, the same month that iOS 10 became available worldwide, the report said.
Adoption is higher in the U.S. than in Canada (14.4%), the U.K. (16.5%) and Germany (19.3%), Adjust said.
"This is trending in a direction where it's not just the tech-savvy, ad-allergic crowd any more," Paul Muller, cofounder and CTO at Adjust, said in a statement. "Marketers will face a large, distributed and worst of all 'unknown' segment of users, especially in places like Germany and the U.S."
Mobile advertising saw $20.7 billion in revenue in 2015, a 66% upswing from the previous year, according to the Interactive Advertising Bureau.