Ssh, Secure Shell, is much more secure than the archaic telnet/rlogin/rsh. You should not remotely access UNIX boxes as an administrator without Ssh. It is bundled with OpenBSD and SuSE Linux. It should be built into all unix OSs. Resources:

• All about SSH
  
• OpenSSH How-To
  
• Exploits
  • Exploit of SSh
    
  • SSH Malformed Packet Vulnerabilities
    
• FAQ Frequently Asked Questions
  • Employees' Ssh FAQ
    
  • Openssh' Ssh FAQ
    
  • Snailbooks' Ssh FAQ
    
• FreeSSH
  
• FSecure
  
• IETF Working Group Secure Shell (secsh)
  
• OpenSSH
  
• OpenSSL
  
• Remote Login Protocol SSH
  
• rssh : restricted shell for OpenSSH
  allowing only scp and/or sftp without providing shell access
• scponly
  ssh-based method to allow remote users to both read and write local files without providing any remote execution priviledges. a wrapper to the "tried and true" ssh suite of applications

• SSH
  
• Tunneling : Corkscrew is a tool for tunneling SSH through HTTP proxies
  
• NT / W2K / XP : SSH for Windows NT / W2K / XP