Tools
-  Host-based Auditing Tools:
 
COPS, NCARP, crack, Tiger, Tripwire, logcheck, tklogger, Safesuite, NetSonar 
 -  Network Traffic Analysis & Intrusion Detection Tools:
 
tcpdump, synsniff, NetRanger, NOCOL, NFR, RealSecure, Shadow 
 -  Security Management and Improvement Tools:
 
crack, localmail, smrsh, logdaemon, npasswd, op, passwd+, S4-kit, sfingerd, sudo, swatch, watcher, wuftpd, LPRng 
 -  Firewall, Proxy amd Filtering Tools:
fwtk, ipfilter, ipfirewall, portmap v3, SOCKS, tcp_wrappers, smapd 
 -  Network-Based Auditing Tools:
 
nmap, nessus, SATAN, Safesuite 
 -  Encryption Tools:
md5, md5check, PGP, rpem, UFC-crypt 
 -  One-Time Password Tools:
 
OPIE, S/Key 
 -  Secure Remote Access and Authorization Tools:
 
RADIUS, TACACS+, SSL, SSH, Kerberos