I configured my FTP service so now I access my NAS from Internet using Filezilla client successfully, the only issue is that Filezilla shows a message that "the server is not secured".
How to secure it?
Enable SSL/TLS connections: Unchecked
Certificate: None (when check "Enable SSL/TLS connections" the drop-down list shows "None" only)
Required: Unchecked: This option requires clients to use FTP over TLS when talking to this server.
No certificate request: Unchecked: This option causes the server to not send a certificate request during a SSL handshake.
No session reuse required: Unchecked: The requirement that the SSL session from the control connection is reused for data connections is not required.
Implicit SSL: Unchecked: This option will handle all connections as if they are SSL connections implicitly.
Extra options: (blank)