> Using XDMCP is inherently insecure, therefore, most of the > distributions shipped as it's XDMCP default turned off. If you > must use XDMCP, be sure to use it only in a trusted networks, > such as corporate network within a firewall. Unfortunately, > XDMCP uses UDP, not TCP, therefore, it is not natively able to > use it with SSH. To secure the connection with SSH, the > technique is called X11 TCP/IP Port Forwarding.