In society, the term hacker has been used as both a compliment and a derogatory term. In its original sense, it is used to describe one who is an expert, a problem solver, and generally a brilliant programmer. In the media and in society, however, the term has come to mean criminals who illegally break into computer networks and systems.
Precursors and the hacker ethic
The term originated at the Massachusetts Institute of Technology (MIT), certainly before computers were available, and probably from the Tech Model Railroad Club. In its original MIT form, it primarily referred to practical jokes that:
- are safe
- do not damage anything
- do not damage anyone, either physically, mentally or emotionally
- are funny, at least to most of the people who experience it
"There is no way of enforcing this code, but anything that directly contradicts it will probably not be considered a "hack" by most of the MIT community."
As computers and networks became more common, a broader ethic emerged, with the principles:
- Access to computers should be unlimited and total.
- Always yield to the Hands-On Imperative
- All information should be free.
- Mistrust authority–promote decentralization.
- Hackers should be judged by their hacking.
- You can create art and beauty on a computer.
- Computers can change your life for the better.
"Ethical hacking" has emerged, including some of the principles in the first list essentially saying "do no harm". One of the most controversial points of the Levy list is "all information should be free." Many owners of personal computers do not believe their personal correspondence or financial records should be free. Organizations may have legal and arguably moral information to protect such things as personal health information, information on criminal investigations in progress, personnel files, and such things as the detailed design of nuclear weapons. The most ethical hacker is not omniscient, and has no way of knowing that the act of access may have unintended consequences. It is true that such things as electrical power grid SCADA controls, and medical radiation therapy machines, should never be accessible from the outside, but, if they are somehow reached, there is real danger from innocent exploration.
Most system and network administrators, once they know there has been access by an unauthorized person, cannot assume that the intruder is ethical, and, as a matter of safety, close the entry point, and possibly shut down legitimate access until the computer(s) return to a known stable state.
Two sides of the Coin
The term "hacker" has at least two meanings.
Hackers as Knowledge Seekers
The original meaning of the term hacker was someone who had great technical knowledge. A hack was something to be proud of, usually described as pushing something beyond its design limits. People who usually "hacked on" certain projects would have descriptive names bestowed upon them, thus someone who wrote a lot of kernel code would come to be called a "kernel hacker," or someone who worked on and was knowledgeable with the Unix operating system would come to be called a "Unix hacker."
Hackers as criminals
The media have generally painted hackers as computer security criminals. Some proponents of the original meaning of the term "hacker" (knowledge seekers) call these people "crackers", to specifically point out these people "crack security." Another term, used on Citizendium, is miscreant.
In some old Western movies the good guys have white hats and the villains have black hats. Sometimes people refer to "black hat" and "white hat" hackers; both are interested in breaking systems, but the black hats are miscreants out for their own fun or profit while the white hats analyze attacks, or even try some attacks, in order to guide defense. Penetration testing is a white hat hacker activity. "Grey hat" is also used.
At the Massachusetts Institute of Technology, the term "hack" takes on a meaning that is more analogous with a practical joke. In that vein, a hacker is someone (or a group of people), usually students, who conceive and execute a "hack." For example, placing a campus police patrol car on the dome of the MIT building is considered an accomplished hack, both for its technical difficulty and the visual humor it provokes. 
Jargon File Definition
How To Become A Hacker by Eric S. Raymond. Describes how to become a hacker in the "traditional sense" - someone with "technical adeptness and a delight in solving problems and overcoming limits"
- Eric S. Raymond. The Cathedral and the Bazaar: Introduction. Retrieved on 2007-04-18.
- Interesting Hacks To Fascinate People: The MIT Gallery of Hacks, The Hacker Ethic
- Levy, Steven, Hackers - Heroes of the Computer Revolution
- "MIT Hacks". Retrieved on 2007-05-05.
- "CP Car on the Great Dome". Retrieved on 2007-05-05.
- Hacker entry in the "Jargon File". Retrieved on 2007-04-09.