A constructive peaceful hacker.

a hacker whose intentions are not criminal or malicious

A hacker with benign intentions. For example, if a hacker encounters a security hole and the first thing he or she does is explain the problem to the people...

A White Hat Hacker is concerned securing computer systems as opposed to exploiting them. They use their skills to find vulnerabilities in software and inform the software vendor. They also provide advice and opinions on security issues as well developing workarounds for widely exploited vulnerabilities. See also Black Hat.

The opposite (and counterpart) of a cracker. A security operative who aims to protect a network from unauthorized intrusion. The term originates from formulaic Westerns where the good guy always wears a white hat.

A white hat hacker, also rendered as ethical hacker, is, in the realm of information technology, a person who is ethically opposed to the abuse of computer systems. Realization that the Internet now represents human voices from around the world has made the defense of its integrity an important pastime for many. A white hat generally focuses on securing IT systems, whereas a black hat (the opposite) would like to break into them — but this is a simplification as a black hat will wish to secure his own machine, and a white hat will have no issues breaking into it in the course of his or her activities.