A method for securing a transportation means against unauthorised use or theft by means of a lock and a terminal that can be operated in a mobile radio network, comprising the following process steps: a) receiving data by the lock via the mobile radio network by means of a communication module of the lock, wherein the data are addressed to the lock using an addressing information item (MSISDN 2) assigned to the communication module, and wherein the data comprise an addressing information item (MSISDN 1) of a terminal and a key information item (TC') stored by the terminal; b) evaluating the data received by the communication module by means of a computer unit of the lock, wherein a comparison unit of the computer unit compares the key information item (TC') of the received data with the key information item gathered in a storage means of the lock; c) executing a control command by means of the computer unit in case of a concordance of the key information items (TC, TC') that have been compared with each other; d) creating a new key information item (TC") by the computer unit of the lock by means of a generation unit of the computer unit; e) storing the new key information item (TC") created by the generation unit of the computer unit of the lock in the storage means of the lock; f) sending the new key information item (TC") from the communication module via the mobile radio network using the addressing information item (MSISDN 1) of the terminal to the terminal; g) storing the new key information item (TC") by the terminal; and h) actuating the lock on the base of the control command by an electromechanical means for locking or unlocking the lock, by encoding control information that can be turned into control commands by the lock using the new key information item (TC") received by the terminal by means of the terminal, sending the encoded control information via the mobile radio network to the lock, and decoding the received encoded control information while using the new key information item (TC") by the lock. a) receiving data by the lock via the mobile radio network by means of a communication module of the lock, wherein the data are addressed to the lock using an addressing information item (MSISDN 2) assigned to the communication module, and wherein the data comprise an addressing information item (MSISDN 1) of a terminal and a key information item (TC') stored by the terminal; b) evaluating the data received by the communication module by means of a computer unit of the lock, wherein a comparison unit of the computer unit compares the key information item (TC') of the received data with the key information item gathered in a storage means of the lock; c) executing a control command by means of the computer unit in case of a concordance of the key information items (TC, TC') that have been compared with each other; d) creating a new key information item (TC") by the computer unit of the lock by means of a generation unit of the computer unit; e) storing the new key information item (TC") created by the generation unit of the computer unit of the lock in the storage means of the lock; f) sending the new key information item (TC") from the communication module via the mobile radio network using the addressing information item (MSISDN 1) of the terminal to the terminal; g) storing the new key information item (TC") by the terminal; and h) actuating the lock on the base of the control command by an electromechanical means for locking or unlocking the lock, by encoding control information that can be turned into control commands by the lock using the new key information item (TC") received by the terminal by means of the terminal, sending the encoded control information via the mobile radio network to the lock, and decoding the received encoded control information while using the new key information item (TC") by the lock. encoding control information that can be turned into control commands by the lock using the new key information item (TC") received by the terminal by means of the terminal, sending the encoded control information via the mobile radio network to the lock, and decoding the received encoded control information while using the new key information item (TC") by the lock.