The feature—blandly dubbed "Intelligent Tracking Prevention," or "ITP 2"— is the second major iteration of its anti-tracking tool, which was first introduced last year. The update prevents marketers from targeting Safari users across the web. For example, someone who visits Nike's website can't be targeted elsewhere on the web, such as Google search or the New York Times website.
The same logic applies when someone abandons items in their shopping cart. Metrics and conversion rates, meanwhile, are likely to remain a mystery with Safari users.
Safari is the dominant browser in the U.S., capturing more than 50 percent market share on mobile. Its efforts to prevent tracking cookies may upend things such as multi-touch attribution, which informs marketers how effective their ad spend is across channels.
"This makes the entire ecosystem, including Facebook and Google, weaker," says Steven Francolla, CEO of identity measurement provider AirDxp. "Many brands I've spoke with are relying on vendors for insights."
The first version of ITP provided companies with a 24-hour grace period to target users or capture data (which also riled trade bodies such as the 4A's, ANA and IAB). Although companies such as Google and Criteo provided workarounds to circumvent this window, Apple has since opted to take a more aggressive stance. It has removed the grace period altogether, says Simon Harris, head of programmatic activation at Dentsu Aegis Network.
"ITP 2 will have a huge impact on attribution when a user is exposed to an online ad while using a Safari browser," Harris says. "This will mean multi-touch attribution, even over a shorter horizon, will not be possible. The workarounds used by many attribution businesses, including Google, will not work." On a scale of one through 10, with 10 having the most severe impact on digital marketing, Harris pegged ITP 2 as "a seven or eight."
"ITP just makes it incredibly difficult to assess the ROI of advertising when a user is exposed to an online ad while using a Safari browser," he says, but adds that he's optimistic that ad tech vendors will eventually find a solution. When that happens is anyone's guess.
Nearly half of the $88 billion spent on digital advertising went toward search last year and the Safari update is already starting to disrupt digital giants like Google.
For instance, the new version makes it more difficult for advertisers to deploy a practice known as remarketing lists for search ads, commonly called RLSA, that allows brands to segment different Google search audiences using their own data. Brands use RLSA to target consumers who visit their website, or abandon items in their shopping cart, through Google search. But "ITP 2 essentially kills the ability to use RLSA in the Safari browser," says Mark Ballard, VP of research at digital agency Merkle.
According to Merkle, the use of RLSA dropped soon after ITP2 came into effect, hitting a seven-month low for the month of September. "The trouble is there are still more questions than answers as to what ITP 2 is going to do," Ballard says. "It may take some months to develop and we have to watch the data to see what comes of it."
Apple did not respond to a request for comment on Thursday.