When you make a mistake on a typewriter with no delete key and no white-out handy, you could back up to the beginning of the error and type "XXXXX" over everyth

When you make a mistake on a typewriter with no delete key and no white-out handy, you could back up to the beginning of the error and type "XXXXX" over everything and start anew on the following word or line. Someone likely carried this forward as an indicator of a mistake (ie. "hacky") and then it stuck from there.