Abstract
In a viral marketing campaign organizations stimulate customers to forward marketing messages to their contacts. To optimize a viral campaign it is necessary to predict how many customers will be reached, how this reach evolves, and how it depends on promotion activities. a new Viral Branching model can provide these results. It is based on insights from epidemiology and the spread of viruses and was adapted to a marketing context and an electronic environment. The model is applied to an actual viral marketing campaign in which over 200,000 customers participated during a six-week period. The results show that the model quickly predicts the actual reach of the campaign and serves as a valuable tool to support marketing decisions related to online campaigns