An advertiser ID is a resettable identifier assigned by a mobile operating system to a device for advertising purposes — Apple's IDFA (Identifier for Advertisers) on iOS and the Google Advertising ID (GAID / AAID) on Android.
Definition
An advertiser ID is a resettable identifier assigned by a mobile operating system to a device for advertising purposes — Apple's IDFA (Identifier for Advertisers) on iOS and the Google Advertising ID (GAID / AAID) on Android. It lets ad platforms and measurement tools recognise the same device across apps for attribution, frequency capping, audience building and conversion measurement, without using a permanent hardware identifier.
The identifier is deliberately user-controllable: it can be reset, which breaks the link to past activity, and it can be withheld entirely. On iOS, App Tracking Transparency requires an app to get explicit permission before accessing the IDFA, and most users decline, so the IDFA is unavailable for the majority of iOS devices.
On Android, users can opt out of the advertising ID, and when they do the app receives a string of zeros.
In context
For iGaming mobile user acquisition, the advertiser ID was the backbone of deterministic install and event attribution — match the ID at click to the ID at install, and you know which campaign produced the player. The iOS restrictions broke that for most iOS traffic, moving measurement to Apple's aggregated SKAdNetwork and to modelled attribution, and making iOS cost-per-FTD figures partly estimated rather than measured.
Android attribution via GAID still works for users who have not opted out, which is the majority.
The practical consequences are that buyers weight Android and web funnels more heavily where the signal is fuller, plan iOS budgets around aggregated and modelled measurement, and lean more on first-party events the operator controls (its own login, its own conversion tracking) rather than on cross-app device identity. Any traffic source or attribution setup that still claims full deterministic iOS attribution should be treated with suspicion, because the platform no longer provides the identifier that would make it possible for most users.
Worked example
An operator's mobile team finds it can deterministically attribute 78% of Android installs via GAID but only 26% of iOS installs post-ATT. It runs iOS acquisition to a modelled cost-per-FTD target using SKAdNetwork conversion values and shifts a larger share of the mobile budget to Android where the numbers are real.
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