Apple's latest iPhone software update will make it a lot harder for advertisers to track you
The current iPhone operating system, iOS 9, already features a "limit ad tracking" option that users can toggle on or off by going to Settings > Privacy > Advertising.
The setting will look the same in iOS 10, but it will act a lot differently.
As the Future of Privacy Forum explains in detail, advertisers can currently target specific groups of iPhone users (such as 18-34-year-old males in London interested in football), identified using their unique ID number, which is known as an IDFA (Identifier for Advertising).
With iOS 9, if a user selected "limit ad tracking,"advertisers would not be able to target this user based on their IDFA as they were considered to have opted out of what is known as "behavioral advertising" (which is when your browsing behavior determines the kinds of ads you see online).
However, some ad tech companies still targeted those users based on their location or used the IDFA to help them track that user as they switched between devices. Some ad tech firms also used the IDFA to help measure the effectiveness of their advertising.
Now, when users opt to "limit ad traffic," their IDFA will simply be represented as "00000000-0000-0000-0000-000000000000." Ad tech companies will have no way of identifying those users - even when their only purpose of doing so was to ensure they weren't serving them too many of the same ads (known as "frequency capping"), measuring whether ads led to sales, or preventing advertising fraud.
For consumers, this element of the software update may well be seen as a victory for user privacy.
But some people within the advertising community have some concerns.
Some people think the change will force ad tech companies to use more "intrusive" tracking methods
Writing for AdExchanger, Alan Chapell, president at law firm Chapell and Associates, said:
"The issues I see with this change is that it breaks legitimate advertising models, forces companies to use more intrusive tracking methods and doesn't necessarily improve user privacy. Perhaps most importantly, Apple's move breaks the implicit promise Apple made to the marketplace many years ago that IDFA would support legitimate business models. That seems like a high price to pay."
As far as "more intrusive tracking methods" are concerned, mobile app marketing tracker Kochava has an idea. Writing on its website, the company says it plans to use a "fingerprint-based matching solution" when the "limit ad tracking" option is selected. Generally, device fingerprint matching within apps works by redirecting users to a measurement URL so the ad tech vendor can collect basic information about the device.
If more ad tech vendors attempted to measure in this way, the new, strengthened "limit ad tracking" setting could end up having the opposite effect to the one Apple intended.
That said, it could prove an unexpected win for ad tech vendors that have developed other identification techniques, which are not as invasive of people's personal data.
Jennifer Lum, cofounder of mobile advertising platform Adelphic, said: "Companies that have developed probabilistic identification techniques that look at multiple data points to identify a user will be able to help marketers build plans to achieve strong coverage for limited ad tracking-on consumers."
It's yet another swipe from Apple against online advertising
It's important to get some perspective here, however. Only around 17% of iPhone users have the "limit ad tracking" function switched on, according to the Future of Privacy Forum.
That still equates to hundreds of millions of users but Gavin Stirrat, managing director of mobile ad tech company Voluum, says there's no reason to believe that the new functionality will encourage more people to apply the limit ad tracking setting.
"Across digital advertising, there's always been a proportion of people (typically 10-20%) who look to turn off tracking through one of the many different ways this is possible. These are the same individuals who are highly unlikely to interact with ads, and so the impact is unlikely to be material," Stirrat said.
Nevertheless, the move is the latest in Apple's direction of travel against the mobile advertising ecosystem.
In June last year, Apple CEO Tim Cook took a huge swipe at ad-driven companies like Google and Facebook, saying in a speech that some of the most prominent Silicon Valley companies had built their businesses by "lulling their customer into complacency about their personal information" and monetizing that data - a model that is "not the kind of company that Apple wants to be."
Last year, Apple's iOS 9 software update also allowed users to block ads on their iPhones for the first time.
This summer, Apple shut down its iAd advertising network.
Now Apple is making it harder to target and track its mobile users using the IDFA system it created.
Stirrat said: "The risk they obviously take here is alienating both developers looking to monetize their content, and consumers who enjoy free content and who could find the quantity and quality of free content available reduced. Or perhaps this is Apple taking back control of what has been a more open ecosystem as they look to explore native monetization opportunities in the iOS walled garden."
Eric Seufert, who runs the mobile advertising blog Mobile Dev Memo thinks that by diminishing the ability for advertising networks to target ads to iPhone users, Apple is building a competitive advantage for its own pool of ad inventory.
Seufert said: "If I'm searching for 'hotel app', Apple doesn't really care if I've ever clicked on a game ad: they know what I want, and, as keeper of the search field, they're in a unique position to serve that ad to me. And while it's not clear if IDFA zeroing will produce casualties in an industry -mobile ad tech - that is ripe for consolidation and pruning, it's certainly clear that one company is an indisputable beneficiary of the change: Apple."