The network was never secure. OpenSSH provides strong authentication, protected network connections, support for wrapping legacy protocols, and improved remote X windows security. The price of this protection is careful consideration of configuration details and the issues with key handling. Being aware of the difficulties should provide a successful integration of OpenSSH into the enterprise.
Consider disabling unsafe network services such as telnetd, ftpd, rlogind, and rshd after the deployment of OpenSSH.