http://en.wikipedia.org/wiki/Astroturfing

Astroturfing is a form of advocacy often in support of a political or corporate agenda designed to give the appearance of a "grassroots" movement. The goal of such campaigns is to disguise the efforts of a political and/or commercial entity as an independent public reaction to some political entity—a politician, political group, product, service or event. The term is a derivation of AstroTurf, a brand of synthetic carpeting designed to look like natural grass.