An estimated 500 million Android phones don’t completely wipe data
when their factory reset option is run, a weakness that may allow the
recovery of login credentials, text messages, e-mails, and contacts,
computer scientists said Thursday.
In the first comprehensive study of the effectiveness of the Android
feature, Cambridge University researchers found that they were able to
recover data on a wide range of devices that had run factory reset. The
function, which is built into Google’s Android mobile operating system,
is considered a crucial means for wiping confidential data off of
devices before they’re sold, recycled, or otherwise retired. The study
found that data could be recovered even when users turned on full-disk
encryption.
I guess FairPhone is affected by this as well. So be aware of this when you decide to give your phone away or sell it.