Astroturfing

Astroturfing is the deceptive practice of hiding the sponsors of an orchestrated message or organization (e.g., political, advertising, religious, or public relations) to make it appear as though it originates from, and is supported by, unsolicited grassroots participants. It is a practice intended to give the statements or organizations credibility by withholding information about the source's financial backers. The implication behind the use of the term is that instead of a "true" or "natural" grassroots effort behind the activity in question, there is a "fake" or "artificial" appearance of support. (Wikipedia)