The Meaning of Hack

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The Meaning of `Hack'

"The word hack doesn't really have 69 different meanings", according to MIT hacker Phil Agre. "In fact, hack has only one meaning, an extremely subtle and profound one which defies articulation. Which connotation is implied by a given use of the word depends in similarly profound ways on the context. Similar remarks apply to a couple of other hacker words, most notably random."

Hacking might be characterized as `an appropriate application of ingenuity'. Whether the result is a quick-and-dirty patchwork job or a carefully crafted work of art, you have to admire the cleverness that went into it.

An important secondary meaning of hack is `a creative practical joke'. This kind of hack is easier to explain to non-hackers than the programming kind. Of course, some hacks have both natures; see the lexicon entries for pseudo and kgbvax. But here are some examples of pure practical jokes that illustrate the hacking spirit:

     In 1961, students from Caltech (California Institute of
     Technology, in Pasadena) hacked the Rose Bowl football game.  One
     student posed as a reporter and `interviewed' the director of the
     University of Washington card stunts (such stunts involve people
     in the stands who hold up colored cards to make pictures).  The
     reporter learned exactly how the stunts were operated, and also
     that the director would be out to dinner later.
     While the director was eating, the students (who called
     themselves the `Fiendish Fourteen') picked a lock and stole a
     blank direction sheet for the card stunts.  They then had a
     printer run off 2300 copies of the blank.  The next day they
     picked the lock again and stole the master plans for the stunts
     -- large sheets of graph paper colored in with the stunt
     pictures.  Using these as a guide, they made new instructions for
     three of the stunts on the duplicated blanks.  Finally, they
     broke in once more, replacing the stolen master plans and
     substituting the stack of diddled instruction sheets for the
     original set.
     The result was that three of the pictures were totally different.
     Instead of `WASHINGTON', the word ``CALTECH' was flashed.  Another
     stunt showed the word `HUSKIES', the Washington nickname, but
     spelled it backwards.  And what was supposed to have been a picture of
     a husky instead showed a beaver.  (Both Caltech and MIT use the beaver
     --- nature's engineer -- as a mascot.)
     After the game, the Washington faculty athletic representative
     said: "Some thought it ingenious; others were indignant."  The
     Washington student body president remarked: "No hard feelings,
     but at the time it was unbelievable.  We were amazed."
This is now considered a classic hack, particularly because revising the direction sheets constituted a form of programming.

Here is another classic hack:

     On November 20, 1982, MIT hacked the Harvard-Yale football game.
     Just after Harvard's second touchdown against Yale, in the first
     quarter, a small black ball popped up out of the ground at the
     40-yard line, and grew bigger, and bigger, and bigger.  The
     letters `MIT' appeared all over the ball.  As the players and
     officials stood around gawking, the ball grew to six feet in
     diameter and then burst with a bang and a cloud of white smoke.
     The "Boston Globe" later reported: "If you want to know the
     truth, MIT won The Game."
     The prank had taken weeks of careful planning by members of MIT's
     Delta Kappa Epsilon fraternity.  The device consisted of a
     weather balloon, a hydraulic ram powered by Freon gas to lift it
     out of the ground, and a vacuum-cleaner motor to inflate it.
     They made eight separate expeditions to Harvard Stadium between 1
     and 5 A.M., locating an unused 110-volt circuit in the stadium
     and running buried wires from the stadium circuit to the 40-yard
     line, where they buried the balloon device.  When the time came
     to activate the device, two fraternity members had merely to flip
     a circuit breaker and push a plug into an outlet.
     This stunt had all the earmarks of a perfect hack: surprise,
     publicity, the ingenious use of technology, safety, and
     harmlessness.  The use of manual control allowed the prank to be
     timed so as not to disrupt the game (it was set off between
     plays, so the outcome of the game would not be unduly affected).
     The perpetrators had even thoughtfully attached a note to the
     balloon explaining that the device was not dangerous and
     contained no explosives.
     Harvard president Derek Bok commented: "They have an awful lot of
     clever people down there at MIT, and they did it again."
     President Paul E. Gray of MIT said: "There is absolutely no truth
     to the rumor that I had anything to do with it, but I wish there
     were."
The hacks above are verifiable history; they can be proved to have happened. Many other classic-hack stories from MIT and elsewhere, though retold as history, have the characteristics of what Jan Brunvand has called `urban folklore' (see FOAF). Perhaps the best known of these is the legend of the infamous trolley-car hack, an alleged incident in which engineering students are said to have welded a trolley car to its tracks with thermite. Numerous versions of this have been recorded from the 1940s to the present, most set at MIT but at least one very detailed version set at CMU.

Brian Leibowitz has researched MIT hacks both real and mythical extensively; the interested reader is referred to his delightful pictorial compendium "The Journal of the Institute for Hacks, Tomfoolery, and Pranks" (MIT Museum, 1990; ISBN 0-917027-03-5). The Institute has a World Wide Web page at http://fishwrap.mit.edu/Hacks/Gallery.html.

Finally, here is a story about one of the classic computer hacks.

     Back in the mid-1970s, several of the system support staff at
     Motorola discovered a relatively simple way to crack system
     security on the Xerox CP-V timesharing system.  Through a simple
     programming strategy, it was possible for a user program to trick
     the system into running a portion of the program in `master mode'
     (supervisor state), in which memory protection does not apply.
     The program could then poke a large value into its `privilege
     level' byte (normally write-protected) and could then proceed to
     bypass all levels of security within the file-management system,
     patch the system monitor, and do numerous other interesting
     things.  In short, the barn door was wide open.
     Motorola quite properly reported this problem to Xerox via an
     official `level 1 SIDR' (a bug report with an intended urgency of
     `needs to be fixed yesterday').  Because the text of each SIDR
     was entered into a database that could be viewed by quite a
     number of people, Motorola followed the approved procedure: they
     simply reported the problem as `Security SIDR', and attached all
     of the necessary documentation, ways-to-reproduce, etc.
     The CP-V people at Xerox sat on their thumbs; they either didn't
     realize the severity of the problem, or didn't assign the
     necessary operating-system-staff resources to develop and
     distribute an official patch.
     Months passed.  The Motorola guys pestered their Xerox
     field-support rep, to no avail.  Finally they decided to take
     direct action, to demonstrate to Xerox management just how easily
     the system could be cracked and just how thoroughly the security
     safeguards could be subverted.
     They dug around in the operating-system listings and devised a
     thoroughly devilish set of patches.  These patches were then
     incorporated into a pair of programs called `Robin Hood' and
     `Friar Tuck'.  Robin Hood and Friar Tuck were designed to run as
     `ghost jobs' (daemons, in Unix terminology); they would use the
     existing loophole to subvert system security, install the
     necessary patches, and then keep an eye on one another's statuses
     in order to keep the system operator (in effect, the superuser)
     from aborting them.
     One fine day, the system operator on the main CP-V software
     development system in El Segundo was surprised by a number of
     unusual phenomena.  These included the following:
        * Tape drives would rewind and dismount their tapes in the
          middle of a job.
        * Disk drives would seek back and forth so rapidly that they
          would attempt to walk across the floor (see walking
          drives).
        * The card-punch output device would occasionally start up of
          itself and punch a lace card.  These would usually jam in
          the punch.
        * The console would print snide and insulting messages from
          Robin Hood to Friar Tuck, or vice versa.
        * The Xerox card reader had two output stackers; it could be
          instructed to stack into A, stack into B, or stack into A
          (unless a card was unreadable, in which case the bad card
          was placed into stacker B).  One of the patches installed by
          the ghosts added some code to the card-reader
          driver... after reading a card, it would flip over to the
          opposite stacker.  As a result, card decks would divide
          themselves in half when they were read, leaving the operator
          to recollate them manually.
     Naturally, the operator called in the operating-system
     developers.  They found the bandit ghost jobs running, and
     gunned them...  and were once again surprised.  When Robin Hood
     was gunned, the following sequence of events took place:
          !X id1
          id1: Friar Tuck... I am under attack!  Pray save me!
          id1: Off (aborted)
          id2: Fear not, friend Robin!  I shall rout the Sheriff
               of Nottingham's men!
          id1: Thank you, my good fellow!
     Each ghost-job would detect the fact that the other had been
     killed, and would start a new copy of the recently slain program
     within a few milliseconds.  The only way to kill both ghosts was
     to kill them simultaneously (very difficult) or to deliberately
     crash the system.
     Finally, the system programmers did the latter -- only to find
     that the bandits appeared once again when the system rebooted!
     It turned out that these two programs had patched the boot-time
     OS image (the kernel file, in Unix terms) and had added
     themselves to the list of programs that were to be started at
     boot time (this is similar to the way MS-DOS viruses propagate).
     The Robin Hood and Friar Tuck ghosts were finally eradicated when
     the system staff rebooted the system from a clean boot-tape and
     reinstalled the monitor.  Not long thereafter, Xerox released a
     patch for this problem.
     It is alleged that Xerox filed a complaint with Motorola's
     management about the merry-prankster actions of the two employees
     in question.  It is not recorded that any serious disciplinary
     action was taken against either of them.


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