Abstract: A card reading machine includes a card reader for reading data on a magnetic card and a device for preventing reading of the data on the magnetic card by illegal card reading devices operatively associated with the card reading machine. The device for preventing may include an oscillator, a driver circuit and a coil for generating electromagnetic signals similar to data on a card. A method for preventing reading of data on a magnetic card by in illegal card reader in operative association with an apparatus having a card reader intended to read the data on the magnetic card includes producing a signal ruining the data collected by the illegal card reader. The apparatus having a card reader may include an insertion slot in which case the method may further include producing the signal near the insertion slot.