This message indicates that you are connecting to a remote host computer that is using version 1 of the Secure Shell protocol (SSH1).
Note that Secure Shell version 2 (SSH2) is a more advanced protocol than the legacy version SSH1. SSH Communications Security considers the SSH1 protocol deprecated and does not recommend its use anymore.
If you choose to accept the SSH1 connection, multiple terminal windows and the File Fransfer operations are not available.
If you do not want to see this message again, select the appropriate SSH1 Connections setting on the Security page of the Settings dialog. For more information on this option, see Section Defining Security Settings.