In Boston's late 50s slang, a "hacker" was someone that tuned muscle cars/hot rods. It's no surprise that the earliest written occurrence of "hacker", in the modern sense, comes from Cambridge.
Woah, I knew illegal cab driving in Baltimore was called “hacking” but never considered the term had old roots. Turns out it all comes from the use of Hackney horses in the 19th century. https://en.wikipedia.org/wiki/Illegal_taxicab_operation