Extremely popular and commonly adopted microblogging service is not only a new form of communication, but also seen as a place for ”fueling” viral marketing. Due to essential openness and growing ubiquity, microblogsphere offers ways to manipulate the trending topics, through arranging a number of ”messengers” who send messages and make a push on maximizing influence propagation. In this paper, we present an initial study on quantifying and characterizing the events referring to viral campaigns launched in microblogsphere. Our study is based on two independent data sets, one corresponds to an event referring to viral campaign and the other can be considered as not planned. We examine collectively dynamic response of the event referring to viral campaign, in comparison with the event not planed. We find the event referring to viral campaign exhibits different evolving pattern from the other event. Top users with extremely high yield of microblogs in the event referring to viral campaign has been proven to account for the exceptional pattern of dynamic response. We further investigate the individual dynamic response and calculate the centrality of top users for quantitative characterization of these users. This work aims to suggest insights into the evolving of events referring to the viral campaign launched in microblogsphere and the behavior pattern of top users in these events who may dominate the event evolving.