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).
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 X'ed them… and were once again surprised. When Robin Hood was X'ed, the following sequence of events took place: