Lies and deceptions are prevalent in our daily lives, yet most people merely guess when attempting to distinguish between lies and truths. In the current research, we examined the validity of the saying that "it takes a thief to know a thief' by showing that it takes a good liar - one high in attachment insecurity - to detect another liar. In Study 1, 68 card players participated in a Bullshit tournament - a card game in which players try to deceive other players while also striving to detect their deceptions. In Study 2 (N = 99), people who cheated on their romantic partner (versus those who did not) were asked to detect cues of infidelity. Results confirmed our expectations and showed that good liars and cheaters, who are usually insecure individuals, are better at detecting lies and dishonesty. These results are discussed from the perspective of social defense theory, highlighting the utility of personality traits that are often deemed maladaptive. (C) 2017 Elsevier Ltd. All rights reserved.