F. Benevenuto, G. Magno, T. Rodrigues, and V. Almeida. Proceedings of the Seventh Annual Collaboration, Electronic messaging, Anti-Abuse and Spam Conference (CEAS), (July 2010)
H. Kwak, C. Lee, H. Park, and S. Moon. Proceedings of the 19th international conference on World wide web, page 591--600. New York, NY, USA, ACM, (2010)