1. A method for identifying source of malicious network messages, said method comprising steps implemented by a computer of: identifying a subset of a multiplicity of source networks, said subset including one or more source networks which have sent messages to one of a plurality of destination locations having a same Internet Protocol (IP) address, wherein identifying said subset comprises: the computer determining for each of said multiplicity of source networks whether there are fewer intervening hops from said each source network to said one destination location than from said each source network to other of said plurality of destination locations; responsive to a determination that there are fewer intervening hops for said each source network of said multiplicity of source networks, the computer identifying said each source network as included in said subset, and responsive to determining there are not fewer intervening hops for said each source network of said multiplicity of source networks, the computer not identifying said each source network as included in said subset; wherein one or more source networks are continuing to send messages to said one destination location, and further comprising a step of sequentially applying filters to block messages from respective source networks in said subset to determine which source network in said subset is sending said messages, wherein one of said source networks in said subset has sent said messages to said one destination location and said messages are malicious.