1. 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 at least one of: presumed good signatures that match, presumed spam signatures that match or the overall volume of messages sent to the system per signature.