The persistent volume is not hidden. An attacker in possession of the device can know that there is a persistent volume on it. Take into consideration that you can be forced or tricked to give out its passphrase.
Read also our instructions to securely delete the persistent volume.
The programs included in Tails are carefully configured with security in mind. If you use the persistence volume to overwrite the configuration of the programs included in Tails, it can break this security or render these programs unusable.
Be especially careful when using the Dotfiles feature.
Furthermore, the anonymity of Tor and Tails relies on making it harder to distinguish one Tails user from another. Changing the default configurations can break your anonymity.
To protect your anonymity and leave no trace, Tails developers select and configure with care programs that work well together. Installing additional programs may introduce unpredictable problems and may break the protections built-in Tails. Tails developers may not want or may not be capable of helping you to solve those problems.
The web browser is a central part in a system like Tails. The plugins included in the browser are carefully chosen and configured with security in mind. If you install other plugins or change their configuration, you can break your anonymity.
Use the persistent volume only when necessary and to the minimum. It is always possible to start Tails without activating the persistent volume. All the features of the persistent volume are optional and need to be explicitly activated. Only the files and folders that you specify are saved.
It is possible to open the persistent volume from other operating systems, but it might break your security. Other operating systems should probably not be trusted to handle sensitive information or leave no trace.