The modern, non "black hat" use of the word originates with the MIT Tech Model Railroad Club (http://www.gricer.com/tmrc/dictionary1959.html) who define "hack" as '1) an article or project without constructive end; 2) work undertaken on bad self-advice; 3) an entropy booster; 4) to produce, or attempt to produce, a hack (3)."

Quite a few words in the "computer geek" lexicon were borrowed from the TMRC.