WordNet (r) 3.0 (2006):

bottom feeder
    n 1: an opportunist who profits from the misfortunes of others

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

bottom feeder
 n.

    1. An Internet user that leeches off ISPs ? the sort you can never provide
    good enough services for, always complains about the price, no matter how
    low it may be, and will bolt off to another service the moment there is
    even the slimmest price difference. While most bottom feeders infest free
    or almost free services such as AOL, MSN, and Hotmail, too many flock to
    whomever happens to be the cheapest regional ISP at the time. Bottom
    feeders are often the classic problem user, known for unleashing spam,
    flamage, and other breaches of netiquette.

    2. Syn. for slopsucker, derived from the fishermen's and naturalists'
    term for finny creatures who subsist on the primordial ooze. (This sense is
    older.)


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

slopsucker
bottom feeder

   /slop'suhk-r/ A lowest-priority task that only runs when the
   computer would otherwise be idle.  Also called a "hungry
   puppy" or "bottom feeder" (after the fishermen's and
   naturalists' term for finny creatures who subsist on the
   primordial ooze).

   One common variety of slopsucker hunts for large prime
   numbers.

   Compare background.

   [Jargon File]

   (2003-09-29)