1. One or more program storage mediums readable by at least a computer having at least one memory and at least one processor, the one or more mediums tangibly embodying one or more programs of instructions executable by the at least one computer to implement a signature-based message filtering system that facilitates spam prevention and protection comprising: a signature assignment component that determines and assigns one or more signatures for an incoming message based in part on at least one hash function; and a signature analysis component that determines a probability that at least a subset of the message's signatures are indicative of spam based in part on a count of presumed spam signatures that match and a count of the overall volume of messages sent to the system per signature, wherein the signature analysis component determines a complaint rate by taking a product of a percentage of recipient complaints by a number of read messages and dividing the product by an overall volume of incoming messages, and based upon how old the read messages are.