Koutrika, G.; Effendi, F. A.; Gyöngyi, Z.; Heymann, P. & Garcia-Molina, H. (2007), Combating spam in tagging systems, in 'AIRWeb '07: Proceedings of the 3rd international workshop on Adversarial information retrieval on the web' , ACM Press, New York, NY, USA , pp. 57--64 .