In one of several meanings of the word in computing, a hacker is a member of the computer programmer subculture originated in the 1960s in the United States academia, in particular around the Massachusetts Institute of Technology (MIT)'s Tech Model Railroad Club (TMRC) and MIT Artificial Intelligence Laboratory. Nowadays, this subculture is mainly associated with the free software movement.
Hackers follow a spirit of creative playfulness and anti-authoritarianism, and sometimes use this term to refer to people applying the same attitude to other fields.
The Jargon File, a compendium of hacker slang, defines hacker as "A person who enjoys exploring the details of programmable systems and stretching their capabilities, as opposed to most users, who prefer to learn only the minimum necessary."  The Request for Comments (RFC) 1392, the Internet Users' Glossary, amplifies this meaning as "A person who delights in having an intimate understanding of the internal workings of a system, computers and computer networks in particular."  These hackers are disappointed (see definition controversy) by the mass media and mainstream public's usage of the word hacker to refer to security breakers, calling them "crackers" instead.
The difference between hackers and crackers, according to them, is that where hackers use their skills and knowledge to learn more about how systems and networks work, crackers will use the same skills to author harmful software (like viruses, trojans, etc.) and illegally infiltrate secure systems with the intention of doing harm to the system. This subculture of hackers doesn't participate in these activities and generally frowns upon them.
Many find this rewording a band-aid on the problem of social acceptance and recognition, as such 2600 Magazine's ethos is to instead concentrate on educating people about the field and related topics rather than disassociation.
Before communications between computers and computer users was as networked as it is now, there were multiple independent and parallel hacker subcultures, often unaware or only partially aware of each others' existence. All of these had certain important traits in common:
These sorts of subcultures were commonly found at academic settings such as college campuses. The MIT Artificial Intelligence Laboratory, the University of California, Berkeley and Carnegie Mellon University were particularly well-known hotbeds of early hacker culture. They evolved in parallel, and largely unconsciously, until the Internet, where a legendary PDP-10 machine at MIT, called AI, that was running ITS, provided an early meeting point of the hacker community. This and other developments such as the rise of the free software movement drew together a critically large population and encouraged the spread of a conscious, common, and systematic ethos. Symptomatic of this evolution were an increasing adoption of common slang and a shared view of history, similar to the way in which other occupational groups have professionalized themselves but without the formal credentialing process characteristic of most professional groups.
Over time, the academic hacker subculture has tended to become more conscious, more cohesive, and better organized. The most important consciousness-raising moments have included the composition of the first Jargon File in 1973, the promulgation of the GNU Manifesto in 1985, and the publication of The Cathedral and the Bazaar in 1997. Correlated with this has been the gradual election of a set of shared culture heroes: Bill Joy, Donald Knuth, Dennis Ritchie, Alan Kay, Ken Thompson, Richard M. Stallman, Linus Torvalds, Larry Wall, and Guido Van Rossum, among others.
The concentration of academic hacker subculture has paralleled and partly been driven by the commoditization of computer and networking technology, and has in turn accelerated that process. In 1975, hackerdom was scattered across several different families of operating systems and disparate networks; today it is largely a Unix and TCP/IP phenomenon, and is concentrated around various operating systems based on free software and open-source software development.
Many of the values and tenets of the free and open source software movement stem from the hacker ethics that originated at MIT and at the Homebrew Computer Club. The so-called Hacker Ethics were chronicled by Steven Levy in Hackers: Heroes of the Computer Revolution and in other texts.
Hacker ethics are concerned primarily with sharing, openness, collaboration, and engaging in the Hands-On Imperative.
The academic hacker subculture is defined by shared work and play focused around central artifacts. Some of these artifacts are very large; the Internet, the World Wide Web, the GNU Project, and the Linux kernel are all hacker creations, works of which the subculture considers itself primary custodian.
The academic hacker subculture has developed a rich range of symbols that serve as recognition symbols and reinforce its group identity. GNU's Gnu, the BSD Daemon, Tux, the Linux penguin, and the Perl Camel stand out as examples. The use of the glider structure from Conway's Game of Life as a general Hacker Emblem has been proposed by Eric S. Raymond.
The academic hacker subculture has an annual ceremonial day—April Fool's. There is a long tradition of perpetrating elaborate jokes, hoaxes, pranks and fake websites on this date, which includes the publication of the annual joke RFC.
The Jargon File has had a special role in acculturating hackers since its origins in the early 1970s. Many textbooks and some literary works shaped the academic hacker subculture; among the most influential are:
While the word hacker to refer to someone who enjoys playful cleverness is most often applied to computer programmers, it is sometimes used for people who apply the same attitude to other fields. For example, Richard Stallman describes the silent composition 4′33″ by John Cage and the 14th century palindromic three-part piece "Ma Fin Est Mon Commencement" by Guillaume de Machaut as hacks. According to the Jargon File, the word hacker was used in a similar sense among radio amateurs in the 1950s, even predating the software hacking community. More recent examples of this usage are: