Nessus Security Scanner

Nessus Security Scanner

http://www.nessus.org
Nessus is a comprehensive security analyzer for NT and UNIX. It
includes Brute Force and Denial of Service attacks to attempt to breach
a system remotely.

Vetescan

http://www.self-evident.com
An underground UNIX vulnerability scanner with extended analysis
capabilities for exploiting CGI scripts, shares, services and finding
buffer overflows.
Cerberus (CIS)
http://www.cerberus-infosec.co.uk/
Current modular NT and SQL vulnerability scanner including registry
attacks. Many of the modular checks were originally found and
exploited by the author of the package.
References
Firewalking - http://www.packetfactory.net/Projects/Firewalk/