Blue Frog
Blue Frog was a freely-licensed anti-spam tool produced by Blue Security Inc. and operated as part of a community-based system which tried to persuade spammers to remove community members' addresses from their mailing lists by automating the complaint process for each user as spam is received.Blue Security maintained these addresses in a hashed form in a Do Not Intrude Registry, and spammers could use free tools to clean their lists.The tool was discontinued in 2006.[1]