"one who keeps out of sight," early 14c., agent noun from lurk (v.). In the internet sense by 1990.
Entries linking to lurker
lurk v.
c. 1300, lurken "to hide, lie hidden," probably from Scandinavian (compare dialectal Norwegian lurka "to sneak away," dialectal Swedish lurka "to be slow in one's work"), perhaps ultimately related to Middle English luren "to frown, lurk" (see lower (v.2)). From late 14c. as "move about secretly;" also "escape observation." Related: Lurked; lurking.