Dictionary.net

(Presumably from "spam", "index") wordspamming."Spamdexing has come a long way from the halcyon days of thesummer of 1995. Back then, all one needed to do was add theword 'sex' a thousand times at the end of a Web page toattract attention from the likes of Lycos. The search-engineoperators caught on fast" -- Andrew Leonard, Hotwired 1996(http://packet.com/packet/leonard/96/32/index3a.html).