In computer and network security, the term miscreant is a preferred neutral term for people who interfere with networks, either by technical attacks or deceptive "human engineering". Hacker, at one time, had no negative connotations; according to Steven Levy, it is slang that originated at the Massachusetts Institute of Technology (MIT) even before computers were widely available. In the old sense, "hacker" simply meant referred to a person so familiar with a mechanism, be it the trains of the Tech Model Railroad Club or of an operating system, that he or she could make an elegant change to its behavior.
Such changes, especially with respect to computers, consisted of only the minimum necessary changes to produce the effect desired, without causing undesirable side effects, such as crashing the system.
See the hacker article for a discussion of the classic rules for the "ethical hacker". Not all owners of computers would agree with some of the precepts of the "hacker ethic"; many people believe certain information, such as their financial records, diary, medical files, etc., are properly private and not something
When some people with "classic hacker" level knowledge started altering data, even as a joke, or preventing or degrading authorized use of computers, those responsible for the computers, or whose work depended on the computers, were rarely amused. Even if the hacker believed his acts were "ethical", the computer owner or user might not — there was a conflict of ethics.
"Cracker" emerged as a term for unauthorized users bypassing access controls and gaining access to a computer that they were not authorized to use. Some of these users, for their own amusement, as a means of protest, or a plethora of other reasons, might alter data (e.g., put the electronic equivalent of graffiti on a web page), or force the system to be unusable.
Over time, some, certainly not all, unauthorized access involved outright criminal behavior. Situations emerged where data was held for ransom, or there was a credible threat that a distributed denial of service attack would be used to disrupt the computer system — unless the intruder was paid "protection money". The latter, if not involving computers but the physical security of people or things, is the crime of extortion.
Given the range of terms in use and their multiple, context-dependent meaning, many professionals in computer and network security use miscreant to describe unauthorized use, without examining the motivations for such use. This shows what might be called a counter-hacker-ethic, where people believe that their acquisition of, or authorized use of, computing resources should be free from interference that they, or owners of the equipment, do not authorize.