Two unrelated apps do not need to share a login to recognize the same advertising identifier.
That is the point of the mobile advertising ID.
On Android, Google describes the advertising ID as a unique, user-resettable and user-deletable identifier supplied for advertising. Apps and advertising SDKs can retrieve a consistent value associated with the device user and use it for advertising functions such as personalization and measurement. See Google Play’s Advertising ID documentation and Android’s Advertising ID developer guide.
That consistency is useful to advertisers.
It is also what makes the identifier capable of linking activity across apps.
One value can join separate event streams
Imagine a weather app reports:
ad_id = ABC123
Later, a game reports:
ad_id = ABC123
A third app reports the same value.
If the same advertising system receives those events, it does not need the three app developers to exchange customer accounts directly.
The common identifier gives the system a join key.
Activity that looked separate at the app level can become one advertising profile at the network level.
The identifier itself does not contain a person’s name, search history, or purchases.
It becomes meaningful because databases attach events and attributes to it.
Resetting or deleting changes the link
Google’s current Android guidance lets users reset or delete the advertising ID through system settings. On supported Google Play services, deleting it causes attempts to retrieve the ID to receive a zeroed value instead. Google also warns developers not to cache the value because a user may reset it. See Google Play’s Advertising ID guidance.
That gives the user a real control.
A reset can break the straightforward continuity between the old identifier and the new one.
It does not guarantee that every company forgets everything it previously knew.
Historical records may remain subject to retention rules and policies, and other signals can create new connections.
The advertising ID is only one bridge
Apps can also recognize logged-in accounts, email addresses, phone numbers, app-specific identifiers, purchase records, IP-derived information, or other device and network signals.
Android itself distinguishes the advertising ID from other identifiers and provides newer privacy controls around advertising systems. See Android’s ad privacy settings.
So disabling one advertising identifier should not be described as a universal invisibility switch.
It removes or weakens one standardized connection.
That distinction matters throughout the Surveillance Economy.
The dangerous part of a dataset is often not any individual row.
It is the column that lets somebody join one table to another.
On mobile devices, the advertising ID was designed to be exactly that kind of column.