Everyone knows your location: tracking myself down through in-app ads

One of the big WTF moments I've had in the "web vs. device" Ad-related privacy journey was realizing that even if you create an "anonymous" account on an app in your phone, your device ID is shared and can be recognized by Ad vendors.

Example:

- You're using a known account on a Mac to search for a shelf to buy

- You're using a anonymous account to browse Reddit on an iPhone

And the shelf Ad pops up on the Reddit feed. Yep, as long as you logged in with a known account on both devices, they're now linked by device id. An all you do on those devices (regardless of the account) can be traced back to you.

I read about this in "Chaos Monkeys" but it never really hit me until this experience.

This is typically just done through IP address. That's why I get ads for my girlfriend's preferred eye cream brand despite the fact that we browse using different devices and the advertiser should have access to that data point.