As I understand it, it's possible to retrieve data stored in SharedPreferences. Therefore it isn't safe. Could anybody advice me on a way to completely secure the data? I know it's possible to encrypt and store the data, but I'm wondering, is there any other way?
Data stored in SharedPreferences, if created with Context.MODE_PRIVATE, is only accessible to your own application.
Though, if the users phone is rooted, then the data can be read by root applications (even if created with Context.MODE_PRIVATE).
There is no way to avoid that, ever. But you can take precautions such as encrypting the data in SharedPreferences.
A good example of this is the SecurePreferences library: https://github.com/scottyab/secure-preferences