A device and a method of preventing pirated copies of computer programs. The device has input and output devices for bidirectional data exchange with an electronic computer and a first memory element containing a data file that can be transferred to the electronic computer over the output device. In addition, a second memory element into which data can be written via the input device is also provided. The method includes the following steps. First, this device is connected to an electronic computer for bidirectional data exchange. Then a first data file containing an electronic key is transferred from the device to the electronic computer. Subsequently a second data file containing an identifier of the electronic computer is copied from the electronic computer to the device.