The commonly used messenger WhatsApp does not delete all your conversations completely even if you use the option “Clear all chats”. It has been found out by the expert Jonathan Zdziarski. He states that the current version of the messenger on iOS preserves backups of online chats despite it has been deleted already. A threat actor can use it for his own purpose if he has access to the device. According to the expert, chats can be deleted completely after the application is uninstalled.
As Zdziarski has explained, WhatsApp marks the record as “deleted” but in fact it remains in the SQLite database which is not cleared on default. While deleting the messages are removed into the “free list” and stored there until new data appears on top. Usually it happens when the database needs extra free space.
In April the encryption was enhanced in WhatsApp. Now not only text messages but also calls, photos and videos are encrypted on default. The system protects data while being transmitted. At the same time staying on the device or iCloud data is not protected as it is not coded. Moreover, it allows having access to messages for law enforcement even though it has been deleted.
More information about messenger WhatsApp is here.