Underground marketing.

As it has become ever harder to reach people between the ages of 12 and 34, advertisers have pushed viral marketing entirely underground, pitching them on the sly and hoping that the message takes and spreads, viruslike, with none of the intended marks knowing the better. This might mean leaving cigarette packs in bars, as tobacco companies have done, or loaning automobiles to ''key influencers,'' as Ford did in 1999, when it placed the Ford Focus with 120 people in five major markets. Or it might mean hiring some of Big Fat's 50 operatives in 30 cities to drink vodka and water at trendy bars.