The Jargon File (version 4.4.7, 29 Dec 2003):

iron box
 n.

    [Unix/Internet] A special environment set up to trap a cracker logging in
    over remote connections long enough to be traced. May include a modified 
    shell restricting the cracker's movements in unobvious ways, and ?bait?
    files designed to keep him interested and logged on. See also back door,
    firewall machine, Venus flytrap, and Clifford Stoll's account in The
    Cuckoo's Egg of how he made and used one (see the Bibliography in Appendix
    C). Compare padded cell, honey pot.


The Free On-line Dictionary of Computing (30 December 2018):

iron box

   [Unix/Internet] A special environment set up to trap a
   cracker logging in over remote connections long enough to be
   traced.  May include a modified shell restricting the
   cracker's movements in unobvious ways, and "bait" files
   designed to keep him interested and logged on.  See also back
   door, firewall machine, Venus flytrap, and Clifford
   Stoll's account in "The Cuckoo's Egg" of how he made and
   used one.  Compare padded cell.

   [Jargon File]