Date Added: May 2010
Spam is still an open problem from the network operator's perspective. The common state-of-the-art strategy to place filters against spam is at the recipient's edge. Although, this strategy largely solves the spam problem from the user's perspective - false positives/negatives may still exist - it cannot prevent spam from traversing the Internet. Consequently, with nowadays around 200 billion spam/day, spam continues to consume large amounts of Internet bandwidth and provokes non-negligible financial loss to network operators. Therefore it becomes imperative to mitigate spam much earlier than at the recipient's edge. This goal has been recently accomplished only partially by placing filters at the edge of a social circle within a social network.