WhatsApp retains and stores chat logs even after those chats have been deleted, according to a post today by iOS researcher Jonathan Zdziarski. Examining disk images taken from the most recent version of the app, Zdziarski found that the software retains and stores a forensic trace of the chat logs even after the chats have been deleted, creating a potential treasure trove of information for anyone with physical access to the device. The same data could also be recoverable through any remote backup systems in place.
In most cases, the data is marked as deleted by the app itself — but because it has not been overwritten, it is still recoverable through forensic tools. Zdziarski attributed the problem to the SQLite library used in coding the app, which does not overwrite by default.