Anurag Garg Roberto Battiti Roberto G. Cascella "May I borrow Your Filter?" Exchanging Filters to Combat Spam in a Community. 489-493 2006 conf/aina/2006 AINA (2) http://doi.ieeecomputersociety.org/10.1109/AINA.2006.1 db/conf/aina/aina2006.html#GargBC06