A method is provided for authenticating micro-processor cards to determine whether a card is a genuine card or a fake card. Authentication is performed by a checking program of at least one card reader terminal. The program sends to each card commands belonging to a standard and public set of commands. The method includes: modifying the checking program in the terminal or terminals, in such a way that the program additionally sends, to each card to be authenticated, at least one additional command, called a secret command, from a set of at least one additional command, pre-inserted into each genuine card, and different from the standard and public set of commands; and a step of detecting authenticity of the card, if the secret command is recognised and/or processed correctly, or the presence of a clone, if the secret command is not recognised and/or is processed wrongly.