Black ice, in William Gibson's Neuromancer universe, refers to a grade of ice (from intrusion countermeasures electronics) which does physical neurological harm to the user who crosses it. It is illegal because it can easily kill a user. However, the targets which black ice would typically defend would be so esoteric and private that anyone who would happen to come about the wrong side of a program of this nature would most certainly deserve what he or she would get. Black ice would typically defend military grade targets such as weapons systems and artificial intelligences. Some console cowboys have managed to garner a reputation for themselves by being flatlined by black ice and living to tell the tale.

See also: white ice, Dixie Flatline, ice, cyberspace