Abstract: The invention relates to a device for preventing unauthorized use of card- or disc-shaped proofs of legitimacy and/or data carriers, such as ATM cards, credit cards and flexible discs, comprising a cover or case-shaped device (1) or the like having at least one pocket or the like adapted to receive at least a portion of at least one card, disc, etc., actuators and control means (4) arranged in said pocket, said control means being adapted to control said actuators and preferably being of the code lock type and comprising one or more means which, when actuated in a certain sequence or in a certain combination, are adapted to control said actuators.The novelty of the invention resides in that said actuators comprise means (17, 20x, 27) which are activatable when an attempt at gaining access is made without proper actuation of said control means and which, in the event of such an attempt at unauthorized access, are adapted to permanently mechanically damage said card, disc etc. and/or the data carried thereon.