In computing, a hacker is any highly skilled computer expert capable of breaking into computer systems and networks using bugs and exploits. Depending on the field of computing it has slightly different meanings, and in some contexts has controversial moral and ethical connotations. In its original sense, the term refers to a person in any one of the communities and hacker subcultures:
Hacker culture, an idea derived from a community of enthusiast computer programmers and systems designers, in the 1960s around the Massachusetts Institute of Technology's (MIT's) Tech Model Railroad Club (TMRC) and MIT Artificial Intelligence Laboratory. The hobbyist home computing community, focusing on hardware in the late 1970s (e.g. the Homebrew Computer Club) and on software (video games,software cracking, the demoscene) in the 1980s/1990s. Later, this would go on to encompass many new definitions such as art, and Life hacking.
Security hacker. People involved with circumvention of computer security.
White hats are hackers employed with the efforts of keeping data safe from other hackers by looking for loopholes and hackable areas. This type of hacker typically gets paid quite well, and receives no jail time due to the consent of the company that hired them.