Viral marketing works because people trust the opinions of their peers. Author and industry expert George Silverman says, "Word of mouth is the most honest advertising medium there is. People don't want to hurt their friends and family and colleagues with bad information."

Comments and recommendations coming from peers will be perceived as reliable even if the information slyly originates from a marketer.

A successful viral marketing campaign also helps consumers cut through the online clutter. With so many advertisers vying for the same customers, a personal recommendation from a friend or colleague will help direct your online audience to your site without much additional effort like a banner or paid search advertisement.

A prime example of how much attention can be drawn from a viral campaign is Burger King's "Subservient Chicken." This campaign was developed to promote Burger King's Tender Crisp Sandwich by creating a microsite where users can type in a command (e.g., sit, fall, take a nap) to a man in chicken suit who will do it on command. Using the tagline "Chicken the way you like it," the campaign created 10 times the publicity and awareness of a traditional campaign, said the Viral Advertising Association.