Scales easily from small to very large. To spread like wildfire, the transmission method must be rapidly scalable from small to very large. The weakness of the Hotmail model is that a free email service requires its own mail servers to transmit the message. If the strategy is wildly successful, mail servers must be added very quickly or the rapid growth will bog down and die. If the virus multiplies only to kill the host before spreading, nothing is accomplished. So long as you have planned how you can add mail servers rapidly, you’re okay. You must build in scalability to your viral model.
A frequently used example of early viral marketing is Hotmail, the free web-based email service launched in 1996 that included in its users' outgoing messages an embedded advertisement and direct link inviting recipients to sign up for an account. This practice led to the fastest growth among user-based media companies at the time. Another example that illustrates how varied viral marketing can be is the ALS Ice Bucket Challenge. The ice bucket challenge existed before The ALS Association utilized it to raise awareness and generate donations, but the massive dissemination on social media of ALS Ice Bucket videos created a worldwide sensation that not only increased ALS awareness tremendously, but also raised $115 million in donations to the Association in the summer of 2014 alone.
Online reviews have become one of the most important components in purchasing decisions by consumers in North America. According to a survey conducted by Dimensional Research which included over 1000 participants, 90% of respondents said that positive online reviews influenced their buying decisions and 94% will use a business with at least four stars. Interestingly, negative reviews typically came from online review sites whereas Facebook was the main source of positive reviews. Forrester Research predicts that by 2020, 42% of in-store sales will be from customers who are influenced by web product research.
According to a paper by Duncan Watts and colleagues entitled: "Everyone's an influencer", the most common risk in viral marketing is that of the influencer not passing on the message, which can lead to the failure of the viral marketing campaign. A second risk is that the influencer modifies the content of the message. A third risk is that influencers pass on the wrong message. This can result from a misunderstanding or as a deliberate move.