The Android Instagram app acquired by Facebook for $1 billion hit 50 million registered users, with 5 million of them in just six days, SlashGear reports.

Previously, the service amassed 30 million users at the beginning of April just before the Facebook purchase, and hit 40 million on April 13. While many were at first questioning the reason why Facebook decided to buy the service, it seems to be for that massive user base, and possibly to nip any potential competition in the bud, the report says.

The majority of users so far seem to be using the iPhone app. The Android application passed the 10 million download mark two days ago, which is impressive growth for an app that’s only a month old. iPhone users didn’t take kindly to the release of the app on Android, with some users frustrated with the new influx of test photos, although most seemed to be an attack on the Android platform itself.