Abstract: A method for securing payment data for transmission over open communication networks is disclosed. The method comprises establishing a data connection between a first and a second transceiver device, the first transceiver device configured as a merchant device and the second transceiver device configured as a customer transceiver device. The merchant device transmits a first data package which comprises a unique merchant identifier and transaction request data, to the customer transceiver device over the data connection. The merchant device receives a cryptogram from the customer transceiver device. The cryptogram having been generated from using a secret key and a counter value together with the received unique merchant identifier and the transaction request data.