Benjamin Kuipers Alex X. Liu Aashin Gautam Mohamed G. Gouda Zmail: Zero-Sum Free Market Control of Spam. 20-26 2005 conf/icdcsw/2005 ICDCS Workshops http://doi.ieeecomputersociety.org/10.1109/ICDCSW.2005.144 db/conf/icdcsw/icdcsw2005.html#KuipersLGG05