R. Baeza-Yates, and C. Castillo. WWW '06: Proceedings of the 15th international conference on World Wide Web, page 927--928. New York, NY, USA, ACM Press, (2006)
E. Friedman, J. Halpern, and I. Kash. EC '06: Proceedings of the 7th ACM conference on Electronic commerce, page 140--149. New York, NY, USA, ACM Press, (2006)
S. Pandit, D. Chau, S. Wang, and C. Faloutsos. WWW '07: Proceedings of the 16th international conference on World Wide Web, page 201--210. New York, NY, USA, ACM Press, (2007)