Vulnerability Scanning:

Every operating system or the services will have some vulnerabilities due to the
programming errors. These vulnerabilities are crucial for a successful hack. Bugtraq is
an excellent mailing list discussing the vulnerabilities in the various system. The
exploit  code writers write exploit codes to exploit these vulnerabilities existing in a system.

There are a number of vulnerability scanners available to scan the host for known vulnerabilities. These vulnerability scanners are very important for a network administrator to audit the network security.

Some of such vulnerability scanners include Shadow Security Scanner,Stealth HTTP Scanner, Nessus, etc. Visit

http://www.securityfocus.com vulnerabilities and exploit codes of various

operating systems. Packet storm security

(http://www.packetstormsecurity.com) is also a nice pick.