Method for authenticating micro-processor cards, intended to determine whether a card is a genuine card, supplied by an authorised distributor, or a fake card, known as a clone, supplied by an unauthorised third party, by means of a checking program of at least one card reader terminal, said program sending to each card commands belonging to a standard and public set of commands, characterised in that, whereby each genuine card, during the manufacture thereof, stores in a command storage memory said standard and public set of commands, and a set of at least one additional, so-called secret command, it comprises: - during a preliminary period, a step of implementing said checking program in at least one card reader terminal, using said standard and public set of commands, for each transaction; and - after detecting cloned cards in circulation: -- a step of receiving, by said one or more card reader terminals, a modified checking program, sending to each card to be authenticated at least one secret command belonging to said set of at least one additional command stored in memory in said one or more genuine cards and not present in the cloned cards; -- a step of implementing said modified checking program in said one or more card reader terminals, for each transaction; -- a step of detecting the authenticity of said card, during a transaction, if said at least one secret command is recognised and/or processed correctly by said card, or the presence of a clone, if said at least one secret command is not recognised and/or is processed wrongly by said card. - during a preliminary period, a step of implementing said checking program in at least one card reader terminal, using said standard and public set of commands, for each transaction; and - after detecting cloned cards in circulation: -- a step of receiving, by said one or more card reader terminals, a modified checking program, sending to each card to be authenticated at least one secret command belonging to said set of at least one additional command stored in memory in said one or more genuine cards and not present in the cloned cards; -- a step of implementing said modified checking program in said one or more card reader terminals, for each transaction; -- a step of detecting the authenticity of said card, during a transaction, if said at least one secret command is recognised and/or processed correctly by said card, or the presence of a clone, if said at least one secret command is not recognised and/or is processed wrongly by said card. -- a step of receiving, by said one or more card reader terminals, a modified checking program, sending to each card to be authenticated at least one secret command belonging to said set of at least one additional command stored in memory in said one or more genuine cards and not present in the cloned cards; -- a step of implementing said modified checking program in said one or more card reader terminals, for each transaction; -- a step of detecting the authenticity of said card, during a transaction, if said at least one secret command is recognised and/or processed correctly by said card, or the presence of a clone, if said at least one secret command is not recognised and/or is processed wrongly by said card.