1. A method of determining if an event is fraudulent, the method comprising: obtaining a plurality of events comprising a plurality of tagged events and one or more untagged events, wherein each tagged event of said tagged events comprises a fraudulent score value indicating a likelihood of whether said tagged event corresponding to said fraudulent score value was fraudulent; determining a similarity weight between each pair of said plurality of events to generate a plurality of similarity weights, said similarity weight indicating a similarity between said events in a given pair, wherein said determining a similarity weight further comprises constructing a undirected graph where each node in said graph corresponds to one of said plurality of events and wherein said plurality of events are connected using weighted links; processing said similarity weights to assign a fraudulent score value to one or more of said untagged events such that said one or more untagged events receive a fraudulent score value based on said fraudulent score values of said tagged events that are similar to said one or more untagged events; and classifying whether at least one of said one or more untagged events is fraudulent based on said assigned fraudulent score values.