Mozilla Foundation:

There is a unique ID living on your iPhone right now that allows advertisers to track the ads you click on, the videos you play, and the apps you install.

The good news is, you can turn this identifier off. The bad news: most people don’t know that feature exists, let alone that they should turn it off. And we don’t think that they should have to.

That’s why we’re asking Apple to change the unique IDs that advertisers use to track us on each iPhone, every month. That means we could still get relevant ads – but there’s a real cap that makes it harder for companies to build profiles of us over time.

From this Apple support page:

To give you the best advertising experience, Apple provides ads in the App Store and Apple News that are based on information such as your App Store search history and Apple News reading history. (Learn more about the information Apple uses to serve advertisements to you.) If you want to opt out of these interest-based ads, you can choose to turn on the Limit Ad Tracking setting on your iPhone, iPad, iPod touch, and Apple TV. You can also turn off Apple’s location-based ads on your iPhone, iPad, and iPod touch.

If this is new to you, follow the instruction on the support page and turn on Limit Ad Tracking on your iOS devices and Apple TV.

But there’s more to this. As Mozilla points out, there’s an advertising identifier that lets advertisers “build profiles of us over time”. To see this, grab your iOS device, head to Settings > Privacy.

Scroll all the way to the bottom, and tap Advertising (did you even know that choice existed?) And there, under the Limit Ad Tracking switch, is the Reset Advertising Identifier button.

With that in mind, go back and read the Mozilla Foundation post. Seems to me, Apple has the right idea with that Limit Ad Tracking switch. As long as it is on by default.

Sidebar: On that same Setting page, tap View Ad Information and About Advertising & Privacy. Given how central privacy has become to Apple’s brand, seems to me this stuff should be a little less hidden, a little more up front.