The etymology of hackish `foo' is obscure. When used in connection with `bar' it is generally traced to the WWII-era Army slang acronym FUBAR (`Fucked Up Beyond All Repair'), later bowdlerized to foobar. (See also FUBAR.)
However, the use of the word `foo' itself has more complicated antecedents, including a long history in comic strips and cartoons. The old "Smokey Stover" comic strips by Bill Holman often included the word `FOO', in particular on license plates of cars; allegedly, `FOO' and `BAR' also occurred in Walt Kelly's "Pogo" strips. In the 1938 cartoon "The Daffy Doc", a very early version of Daffy Duck holds up a sign saying "SILENCE IS FOO!"; oddly, this seems to refer to some approving or positive affirmative use of foo. It has been suggested that this might be related to the Chinese word `fu' (sometimes transliterated `foo'), which can mean "happiness" when spoken with the proper tone (the lion-dog guardians flanking the steps of many Chinese restaurants are properly called "fu dogs").
Paul Dickson's excellent book "Words" (Dell, 1982, ISBN 0-440-52260-7) traces "Foo" to an unspecified British naval magazine in 1946, quoting as follows: "Mr. Foo is a mysterious Second World War product, gifted with bitter omniscience and sarcasm."
Other sources confirm that `FOO' was a semi-legendary subject of WWII British-army graffiti more-or-less equivalent to the American Kilroy. Where British troops went, the graffito "FOO was here" or something similar showed up. Several slang dictionaries aver that FOO probably came from Forward Observation Officer. In this connection, the later American military slang `foo fighters' is interesting; at least as far back as the 1950s, radar operators used it for the kind of mysterious or spurious trace that would later be called a UFO (the older term resurfaced in popular American usage in 1995 via the name of one of the better grunge-rock bands).
Earlier versions of this entry suggested the possibility that hacker usage actually sprang from "FOO, Lampoons and Parody", the title of a comic book first issued in September 1958, a joint project of Charles and Robert Crumb. Though Robert Crumb (then in his mid-teens) later became one of the most important and influential artists in underground comics, this venture was hardly a success; indeed, the brothers later burned most of the existing copies in disgust. The title FOO was featured in large letters on the front cover. However, very few copies of this comic actually circulated, and students of Crumb's `oeuvre' have established that this title was a reference to the earlier Smokey Stover comics.
An old-time member reports that in the 1959 "Dictionary of the TMRC Language", compiled at TMRC, there was an entry that went something like this:
FOO: The first syllable of the sacred chant phrase "FOO MANE PADME HUM." Our first obligation is to keep the foo counters turning.For more about the legendary foo counters, see TMRC. Almost the entire staff of what later became the MIT AI Lab was involved with TMRC, and probably picked the word up there.
Very probably, hackish `foo' had no single origin and derives through all these channels from Yiddish `feh' and/or English `fooey'.