Ask HN: How does uber automatically log me in after I redownload the app? - taigeair
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devmgr12345
Related: if you register for push notifications, Apple/Google have a habit of
sending you the same push token as you received on that device previously.
It's not guaranteed (and should be insufficient for login), but this does make
it possible to track users across app reinstalls.

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a_lifters_life
Its possible they leave a persistent cookie on your device, even after
'deleting the app'

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gtirloni
It has USB media access and thus can edit your files. They probably choose not
to delete that data during uninstall.

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symlinkk
if you sign in with your facebook / twitter account it uses the system-wide
ios facebook / twitter credentials which aren't deleted when the app is
removed

