Abstract: The disclosure is directed to determining a social signature of a user of an application, e.g., a social networking application. The social signature can be a representation of social properties of a person, and can be determined based on various factors, e.g., user profile of the user and friends of the user. The social signature can be used for various applications, e.g., determining socially similarity of a user pair and determining if a user is a spammer. The social signature is determined as a vector of k buckets in which each of the k buckets indicates a count of friends of the user assigned to the corresponding bucket. A social similarity of a user pair is determined as a function of the social signatures of the user pair. A user is determined as likely to be a spammer if the social signature of the user is of a specified pattern.