The focus of viral marketing is the fact that it has the ability to replicate itself without any outside assistance. A viral marketing campaign is one which allows and motivates customers who are exposed to the campaign to actively help spread the word themselves.
Your customers pass on the word to other potential customers either because of their excitement about the clothing brand, because of what you are offering, or worth sharing as the result of a gift or award option associated with the campaign.
Having such a built-in replication capability, viral marketing has the potential for exponential growth and can quickly spread a message to thousands or even millions of people from just one simple starting point. A great case study of viral marketing is Hotmail. Hotmail.com, was one of the first free web based e-mail services. They recruited members by first giving away free e-mail addresses, then requiring that every e-mail sent by their service include an advertisement at the bottom for their free e-mail service.
This strategy had their free service quickly spread through exponential growth and grew a large member base to be tapped for marketing other services also. Some viral strategies are obviously going to work better than others. The Hotmail campaign in which free services are offered with no cost for the users, are positioned to grow fast.
The key to success for viral marketing is delayed gratification. The company may not profit today or even tomorrow, but can generate a groundswell of interest. Eventually the profits will come and hopefully for a long time afterwards. Investing up front by providing something for free will attract attention that can be redirected to other items you are selling and eventually earn money.
In the real world a virus only spreads when allowed to transmit from one person to another. Likewise, your marketing message must rely on existing mechanisms through which the message is just as easy to transfer and replicate: e-mail, social networks, etc.
Viral marketing works so well on the Internet because of the ease of instant inexpensive communication and because people like to share things. From a marketing standpoint, your goal is to simplify your message so it can be spread easily and the shorter the better.