The Meaning of 'Hack'

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 docu<i></i>mentation, 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.