Signal is a communication app that prides itself on offering encrypted messaging, but fails to provide that same protection when performing an upgrade from its Chrome extension to the desktop version. Security researcher Matt Suiche noticed that the app dumped the information in a location of his choosing without encrypting it first. Signal Desktop is also bad at removing media that has been attached to disappearing messages – a feature that deletes messages from the devices involved in a conversation after a specific amount of time. Users have to delete the folders manually to lower the risk of leaking their private conversations.
Source: https://www.bleepingcomputer.com/news/security/signal-upgrade-process-leaves-unencrypted-messages-on-disk/