Localytics uses different methods for attribution depending on your app's platform, your advertising partners, and which attribution methodology you are using.
For third-party attribution, Localytics uses IDFA on iOS and either Android ID or GAID on Android (depending on which identifier your third-party attribution partner provides).
On iOS, Localytics uses IDFA to conduct Localytics-native attribution.
On Android, Localytics uses GAID to conduct attribution for Twitter and Facebook-acquired users (sometimes in conjunction with the Facebook attribution identifier if that is available). Localytics uses the Google Play Store's Android referrer parameters to perform attribution for other ad partners.