The advertising ID is a unique anonymous identifier on Android devices that is being used for advertising purposes.
App developers can use the advertising ID API to access the ID on user devices, for instance to identify users and devices for targeted advertising.
It is only used by applications offered on Google Play and the only allowed persistent identifier for all advertising purposes.
It needs to be noted that older Android versions may not support the advertising ID and that app developers may fall back to using other methods such as using the Android ID to track users anonymously on Android.
It allows developers (and Google) to create anonymous user profiles based on the ID to deliver targeted advertising to Android users.
While there is no option to turn the ID off Android, options to reset are provided.
Reset your Android advertising ID
Step 1: Open Google Settings on your Android device by tapping on menu and then on Google Settings once all apps are displayed on the screen.
Step 2: Locate and tap on the Ads menu under Services.
Step 3: Tap on "reset advertising ID" on the new page. The page lists the current advertising ID on the same page.
Step 4: Confirm the reset when the confirmation prompt is displayed. Once you reset the advertising ID, a new ID is displayed immediately on the same page. Since a new ID is assigned now, advertisers cannot link past actions anymore to the device if only the advertising ID was used for that.
Step 5 Bonus: Opt-out of interest-based ads as well on the same page. This tells apps not to use the advertising ID for tracking purposes and to only show regular advertisement but not interest-based ads on the device.
According to Google, apps must check the settings of the Android device and respect them. If interest-based ads are disabled on the device, apps must honor that. Failure to do so is a policy violation.
The content policy page offers additional information on how the advertising ID may be used by companies or developers.
It states that companies may not link the advertising identifier to personal identifiable information or persistent device identifiers such as the IMEI or Mac address of the device without explicit consent.
Companies who use the advertising identifier need to disclose this in public privacy notifications.