1. Navicat's connection information is stored in Windows Registry (Windows version) or a file (Mac and Linux versions). The registry or the file is only accessible by the user who logged into the computer. Other user accounts from the same the computer cannot access it. And, the database server's password inside is encrypted.
Windows - HKEY_CURRENT_USER/Software/PremiumSoft/
Mac - ~/Library/Application Support/PremiumSoft CyberTech/preference.plist
Linux - /root/.navicat/user.reg
2. Navicat does not contain any backdoors. It will not send user computer information or login information to anywhere.
3. By default, Navicat's query files, backup files, database models etc are stored in the default settings location and profile location folders which can only be accessed by the user who logged into the computer. Other users from the same computer cannot access those folders.