A Game-Theoretic Investigation of the Effect of Human Interactive Proofs on Spam E-mail.

We show how a game-theoretic model of spam e-mailing, which we had introduced in previous work, can be extended to include the possibility of employing Human Interactive Proofs (hips) in conjunction with filters that classify incoming messages as legitimate or spam. Using our extended model, we show that making hips widely available to e-mail users will reduce the volume of spam on the Internet and increase the benefit that legitimate users obtain from e-mail.