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(jargon.info)OS and JEDGAR

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:OS and JEDGAR:
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This story says a lot about the ITS ethos.

On the ITS system there was a program that allowed you to see what was
being printed on someone else's terminal.  It spied on the other guy's
output by examining the insides of the monitor system.  The output spy
program was called OS.  Throughout the rest of the computer science
(and at IBM too) OS means `operating system', but among old-time ITS
hackers it almost always meant `output spy'.

OS could work because ITS purposely had very little in the way of
`protection' that prevented one user from trespassing on another's
areas.  Fair is fair, however.  There was another program that would
automatically notify you if anyone started to spy on your output.  It
worked in exactly the same way, by looking at the insides of the
operating system to see if anyone else was looking at the insides that
had to do with your output.  This `counterspy' program was called
JEDGAR (a six-letterism pronounced as two syllables: /jed'gr/), in
honor of the former head of the FBI.

But there's more.  JEDGAR would ask the user for `license to kill'.
If the user said yes, then JEDGAR would actually {gun} the job of the
{luser} who was spying.  Unfortunately, people found that this made
life too violent, especially when tourists learned about it.  One of
the systems hackers solved the problem by replacing JEDGAR with
another program that only pretended to do its job.  It took a long
time to do this, because every copy of JEDGAR had to be patched.  To
this day no one knows how many people never figured out that JEDGAR
had been defanged.

Interestingly, there is still a security module named JEDGAR alive as
of late 1994 -- in the Unisys MCP for large systems.  It is unknown to
us whether the name is tribute or independent invention.