1. A method for an advertiser to associate an advertisement published on a plurality of Internet websites on the world wide web comprising: a) obtaining from the advertiser at least one of the advertisement and a keyword string corresponding to the advertisement; b) deriving a contextual information regarding the advertisement from the at least one of the advertisement and the keyword string corresponding to the advertisement; c) comparing the contextual information regarding the advertisement with a set of pre-defined categories; d) determining one or more pre-defined categories from the set of pre-defined categories based on at least one of an amount of content in each of the pre-defined categories and a demographic data corresponding to a plurality of users viewing a plurality of contents in the pre-defined categories; and e) conveying the one or more pre-defined categories to the advertiser, wherein the advertiser associates the advertisement published on the plurality of Internet websites on the world wide web belonging to the one or more pre-defined categories.