I saw a couple of posts today, comment on the recent increase in spam, incuding this one from Ed Felten. Felten, not surprisingly, hits the nail on the head. Despite overly optimistic predictions to the contrary, spam will continue to thrive as long as the payoff outweighs the cost. Much like information security, as long as there is an incentive, spammers will continue to mutate and try to out adapt blockers. Also like security, spammers have an advantage in that all they need is a single successful technique at a time while blockers can only ever hope to play catch up. The success of botnets, as Felten identifies, adds a new dimension where dealing with spam has much to do with the messages themselves as it does with security, making the defenders job that much harder, if not asymptotically approaching impossible.