An Ethical Hacker is one name given to a Penetration Tester. An ethical hacker is usually employed by an organization who trusts him to attempt to penetrate networks and/or computer systems, using the same methods as a hacker, for the purpose of finding and fixing computer security vulnerabilities. Illegal hacking (i.e.; gaining unauthorized access to computer systems) is a crime in most countries, but penetration testing done by request of the owner of the targeted system(s) or network(s) is not, except in Germany.
A Certified Ethical Hacker has obtained a certification in how to look for the weaknesses and vulnerabilities in target systems and uses the same knowledge and tools as a hacker.
The certification is in Version 6 as of August 2008.
The EC-Council offers another certification, known as (CNDA). This certification is designed for United States Government Agencies, and is available only to members of selected agencies. Other than the name, the content of the course is exactly the same. The exam code for CNDA is 312-99.