. https://www.wired.com/story/ad-id-ios-android-tracking/

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SHARESHARESHARE
A SIMPLE WAY TO MAKE IT HARDER FOR MOBILE ADS TO TRACK YOU
If you're not careful, most of what you do online and in mobile apps will wind up fueling targeted advertising, all that data feeding into a composite profile of your likes, dislikes, and demographic information. But increasingly, even careful web users can't avoid being swept up in the digital marketing dragnet. While it's ridiculously difficult to get a handle on all this tracking, there is a simple step you can take right now to throw a tiny wrench in those industry-wide gears. Both Android and iOS force apps to use a special "ad ID" for tracking smartphones, which gets linked to whatever data marketers collect from you. But the benefit of having a designated ad ID is that iOS and Android both allow you to reset it or zero it out. This means that with just a few taps on either platform, you can disrupt the profiles ad networks have collected about you, and keep them from growing any more, by turning on a feature in both Android and iOS that essentially sends out a dummy ID that's all zeros. If you turn this on, you'll stop the tracking that apps were coordinating through your ad ID. READ MORE