What is a criminal hacker?

Originally the term referred to people who used a razor blade and/or fingernail clippers to "hack" or roughly cut parts in electronics such as the traces on circuit boards, legs of diodes etc. Police scanners were "hacked" in order to add more memory, remove CPU processors , speed up scanning by "hacking" the crystal oscillator and replacing with faster ones. Thes methods are directly related to why computers now have more RAM, and are faster. Some of the old (and I do mean old) "hackers" devised a system in the 1960s to simultaneously send voice and data over a phone line using frequency phase shifting and filtering. A similar process used later by DSL.

"Hacking" and "Modding" evolved into things such as examining the programming of a thing. Beginning with noticing things such that by pressing certain keys or combinations of keys in certain secquences on a device could produce certain results. Following the era of IBM's "Big Blue" Chess tournament, AT&T introduced the "unbeatable Tic Tac Toe Computer, and exhibited it. I, I mean a "hacker" back then, was able to beat the computer with a sequence of key presses in order to "cheat" the computer out of a move. On many Shortwave radiOS, Police Scanners, even cell phones etc, certain key presses are used in the programming, and could be used to alter that programming.

The keys on a keyboard of a device are a "Matrix" Keyboards use a matrix with the rows and columns made up of wires. Each key acts like a switch. When a key is pressed, a column wire makes contact with a row wire and completes a circuit. The keyboard controller detects this closed circuit and registers it as a key press to the software.

I'm going to try to keep this understandable to readers ...

Software can emulate or act like hardware.

Example: a hardware modem versus a DSP/Digital Signal Processor modem, where a chip is programmed to act like the hardware....

So, later, the focus turned even more from "hacking" the actual electronics and hardware to software "hacking" through PROGRAMMING.

A "black hat" hacker is often referred to as a microcomputer user who attempts to gain unauthorized access to proprietary computer systems. Although that could be a "cracker" ... a person cracking passWords etc.

Most often people who call themselves "hackers" are called "wannabes" by the old-timers, and nowadays are often adolescents using a program they didn't write, by clicking a button they didn't create, to do what don't understand, in an attempt to disrupt something they don't know how to fix.

"White Hat" hackers are the "good guys" like ... Like the old-timers who vastly improved what computers are capable of doing, and the ones currently trying to improve security by locating and preventing weaknesses.

This Answer is dedicated to the memory of Bill Cheek, author, The Scanner Modification Handbook series, and his BBS and Fidonet terminal (prior to "The internet") Good man, Good freind to many... May he R.I.P.