Well, the original definition of the word "hacking".
Hacking on keyboard to exploit keypress timings, key combinations and key buffer overflows.
( see also http://catb.org/~esr/jargon/html/index.html and https://en.wikipedia.org/wiki/Jargon_File )
"Cracker" is the term used commonly - as in "crack the nut"; i.e. gain access to systems / break copy protection etc. Then you have the phone guys, the phreakers, whistling for free calls.
Hmm. Right spirit but not so much "hacking code together" going on at MIT's Tech Model Railroad Club in 1958.
"a project undertaken or a product built not solely to fulfill some constructive goal but with some wild pleasure taken in mere involvement, was called a `hack'".
(Steven Levy, "Hackers").
HACK: 1) something done without constructive end;
2) a project undertaken on bad self-advice;
3) an entropy booster;
4) to produce, or attempt to produce, a hack.
I saw this as a term for an unconventional or unorthodox application of technology, typically deprecated for engineering reasons. There was no specific suggestion of malicious intent (or of benevolence, either). Indeed, the era of this dictionary saw some "good hacks:" using a room-sized computer to play music, for instance; or, some would say, writing the dictionary itself. HACKER: one who hacks, or makes them.
A hacker avoids the standard solution. The hack is the basic concept; the hacker is defined in terms of it.----
[1] "An Abridged Dictionary of the TMRC Language", 1959: http://www.gricer.com/tmrc/dictionary1959.html