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

crawling horror
 n.

    Ancient crufty hardware or software that is kept obstinately alive by
    forces beyond the control of the hackers at a site. Like dusty deck or 
    gonkulator, but connotes that the thing described is not just an
    irritation but an active menace to health and sanity. ?Mostly we code new
    stuff in C, but they pay us to maintain one big FORTRAN II application from
    nineteen-sixty-X that's a real crawling horror....? Compare WOMBAT.

    This usage is almost certainly derived from the fiction of H.P. Lovecraft.
    Lovecraft may never have used the exact phrase ?crawling horror? in his
    writings, but one of the fearsome Elder Gods that he wrote extensively
    about was Nyarlethotep, who had as an epithet ?The Crawling Chaos?.
    Certainly the extreme, even melodramatic horror of his characters at the
    weird monsters they encounter, even to the point of going insane with fear,
    is what hackers are referring to with this phrase when they use it for
    horribly bad code. Compare cthulhic.


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

crawling horror

    Ancient crufty hardware or software that is kept
   obstinately alive by forces beyond the control of the hackers
   at a site.  Like dusty deck or gonkulator, but connotes
   that the thing described is not just an irritation but an
   active menace to health and sanity.  "Mostly we code new stuff
   in C, but they pay us to maintain one big Fortran II
   application from nineteen-sixty-X that's a real crawling
   horror."

   Compare WOMBAT.

   [Jargon File]

   (1994-12-01)