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John the ripper
A portable password cracker with built-in efficient implementations of multiple
password hashing algorithms found on various Unix flavors.

Jargon File
The Jargon File is a glossary of hacker slang. The original Jargon File was a collection of hacker slang from technical cultures including the MIT AI Lab, the Stanford AI Lab (SAIL), and others of the old ARPANET AI/LISP/PDP-10 communities including Bolt, Beranek and Newman (BBN), Carnegie-Mellon University (CMU), and Worcester Polytechnic Institute (WPI).

Jerusalem (Also called Israeli; Friday the 13th; PLO)
This virus is a memory resident COM and EXE infector.  It was first discovered at the Hebrew University in Jerusalem in the fall of 1987.  It contains a flaw which makes it re-infect EXE files over and over until the files become too big to fit into memory.  The virus re-directs interrupt 8 (among others) and one-half hour after an infected program loads, the new timer interrupt introduces a delay which slows down the processor by a factor of about 10.  On every Friday the 13, the virus deletes every program executed during the day.

Jerusalem-B
This virus is identical to the Jerusalem except it is able to successfully identify pre-existing infections in EXEfiles and will only infect them once.

Jerusalem-C (Also called the New Jerusalem)
This virus is identical to Jerusalem-B except that the timer interrupt delay code has been bypassed.  This virus is virtually invisible until it activates.