Penetration testing refers to authorized hacking against networks and systems in order to uncover vulnerabilities. Penetration testers report findings to the system owner, allowing for the implementation of enhanced controls.
The EC-Council's Certified Ethical Hacker program provides training and certification for penetration testing. Common methods used in penetration testing include:
References:
http://www.penetration-testing.com/home.html
http://www.oissg.org/wiki/index.php?title=PENETRATION_TESTING_METHODOLOGY