There is a fun anecdote about how to beat tit-for-tat by using a collusion strategy. What you do is enter a team of bots, and their strategy is as follows: 1.

There is a fun anecdote about how to beat tit-for-tat by using a collusion strategy. What you do is enter a team of bots, and their strategy is as follows: 1. For the first 50 rounds, behave according to a predefined sequence. 2. If your opponent also does this sequence, then cooperate in every subsequent round. Otherwise defect in every subsequent round. I don't have a reference on hand, but from what I remember this defeated all other algorithms by a large margin in one of the main yearly Prisoner's Dilemma tournaments.