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.

• Anti-spam techniques (e-mail)
• Collactive, founded by the Blue Security team.
• Malware

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• Krebs, Brian (May 17, 2006), "Blue Security Kicked While It's Down", The Washington Post, archived from the original on June 12, 2006 on the spammers victory and its implications.
• Singel, Ryan (May 16, 2006), "Under Attack, Spam Fighter Folds", Wired News.
• Underwood, Todd (May 8, 2006), "The Blue Security Fiasco", Renesys, archived from the original on June 18, 2006.

• Berinato, Scott (November 2006), "Attack of the Bots. The latest threat to the Net: autonomous software programs that combine forces to perpetrate mayhem, fraud, and espionage on a global scale. How one company fought the new Internet mafia – and lost", Wired, vol. 14, no. 11 on botnets and the DDoS attack on Blue Frog, Oct 31, 2006.
• Brand, Madeleine; Reshef, Eran (17 May 2006), "Spammers Win, Anti-Spam Software Firm Shuts Down", Day to Day (transcript) (interview), NPR.
• Montan, Eric, Spammer Desperately Tries to Undermine Blue Security, archived from the original on January 16, 2017.
• Krebs, Brian (May 17, 2006), "In the Fight Against Spam Email, Goliath Wins Again", The Washington Post.
• Ranum, Marcus J, "Enabling the Complaint Department", Ranum (editorial).
• KnujOn – Another anti-spam service, "a multi-tiered response to Internet threats, specifically email-based threats"
• Suspects in the DDOS attack