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

Great Worm
 n.

    The 1988 Internet worm perpetrated by RTM. This is a play on Tolkien
    (compare elvish, elder days). In the fantasy history of his Middle
    Earth books, there were dragons powerful enough to lay waste to entire
    regions; two of these (Scatha and Glaurung) were known as ?the Great Worms?
    . This usage expresses the connotation that the RTM crack was a sort of
    devastating watershed event in hacker history; certainly it did more to
    make non-hackers nervous about the Internet than anything before or since.


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

Internet Worm
Great Worm

    The November 1988 worm perpetrated by
   Robert T. Morris.  The worm was a program which took
   advantage of bugs in the Sun Unix sendmail program,
   Vax programs, and other security loopholes to distribute
   itself to over 6000 computers on the Internet.  The worm
   itself had a bug which made it create many copies of itself on
   machines it infected, which quickly used up all available
   processor time on those systems.

   Some call it "The Great Worm" in a play on Tolkien (compare
   elvish, elder days).  In the fantasy history of his Middle
   Earth books, there were dragons powerful enough to lay waste
   to entire regions; two of these (Scatha and Glaurung) were
   known as "the Great Worms".  This usage expresses the
   connotation that the RTM hack was a sort of devastating
   watershed event in hackish history; certainly it did more to
   make non-hackers nervous about the Internet than anything
   before or since.

   (1995-01-12)