Blocked root app can edit database in /data/data/

I want to make an app which can send whatsapp messages. So i already have an app which can edit the database in whatsapp. I've used the standard SQLiteOpenHelper. But i wonder, how the database can be accessed even if I block root for my app. It still can edit the database of whatsapp. Is it just a mistake of my ROM and device or is it always possible? My ROM is CyanogenMod 12.1 for Samsung Galaxy S3. And if its just possible on my device, however, how can I get it work on other devices (with root)?