From "The Story of English" McCrum,Cran and MacNeill p.242
"At the fontier itself, whiskey was traded unmixed,and often used to corrupt the local
Indians. Congress tried to regulate the worst excesses of the liquour tradebut the pioneers
tuned to bootlegging (the whiskey would be sold illegally to the Indians in a flat
bottle that could literally be carried in the leg of a boot). Bootleg in the sense of an
unauthorized sale, has now become part of the language wkith phrases like "the bootleg album."