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WhatsApp Isn't Fully Deleting Its 'Deleted' Chats (theverge.com)
Facebook-owned messaging app WhatsApp retains and stores chat logs even after those messages have been deleted, according to iOS researcher Jonathan Zdziarski. The Verge reports: 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. WhatsApp was applauded by many privacy advocates for switching to default end-to-end encryption through the Signal protocol, a process that completed this April. But that system only protects data in transit, preventing carriers and other intermediaries from spying on conversations as they travel across the network.
In SQLite, you can do "PRAGMA secure_delete=ON;" and it will subsequently overwrite all deleted information with zeros. This is turned off by default because it does more disk I/O. Alternatively, one can run "VACUUM" at any time to ensure that all deleted content has been purged from the database file.