Normally such a back door could be removed by removing it from the
source code for the compiler and recompiling the compiler. But to
recompile the compiler, you have to *use* the compiler --- so
Thompson also arranged that the compiler would *recognize when
it was compiling a version of itself*, and insert into the
recompiled compiler the code to insert into the recompiled `login'
the code to allow Thompson entry --- and, of course, the code to
recognize itself and do the whole thing again the next time around!
And having done this once, he was then able to recompile the
compiler from the original sources, leaving his back door in place
and active but with no trace in the sources.

The talk that revealed this truly moby hack was published as
"Reflections on Trusting Trust", `Communications of the
ACM 27', 8 (August 1984), pp. 761--763.

Syn. {trap door}; may also be called a `wormhole'. See also
{iron box}, {cracker}, {worm}, {logic bomb}.

:backbone cabal: n. A group of large-site administrators who pushed
through the {Great Renaming} and reined in the chaos of {USENET}
during most of the 1980s. The cabal {mailing list} disbanded in
late 1988 after a bitter internal catfight, but the net hardly
noticed.

:backbone site: n. A key USENET and email site; one that processes
a large amount of third-party traffic, especially if it is the home
site of any of the regional coordinators for the USENET maps.
Notable backbone sites as of early 1991 include uunet and the
mail machines at Rutgers University, UC Berkeley, DEC's Western