A method for outputting confidential data via an output device of a landline telephone, comprising: - providing the confidential data in a first data-processing device which is assigned to a service provider, wherein the confidential data are assigned to a personalized data-processing operation in the first data-processing device; - storing the confidential data in a storage device, from which at least the first data-processing device is capable of retrieving data; - providing secret data which represent a secret agreed upon between the service provider and a person to whom the personalized data-processing operation is assigned, in the first data-processing device; - transmitting message data from the first data-processing device to a second data-processing device, which is assigned to a message service provider and is configured to transmit received message data to one or more landline telephones in a network of landline telephones, wherein the message data comprise the following: - the confidential data, - the secret data and - receiver data which indicate a landline telephone in the network of landline telephones as receiving device; - querying the secret via the landline telephone in response to an evaluation of the message data by the second data-processing device; - receiving user input data in the landline telephone via an input device of the landline telephone; - transmitting the user input data from the landline telephone to the second data-processing device; - evaluating the user input data by the second data-processing device; - transmitting the confidential data from the second data processing device to the landline telephone, if it is determined during evaluation that the user input data correctly indicate the secret agreed upon between the service provider and the individual; and - outputting the confidential data via an output device of the landline telephone. - providing the confidential data in a first data-processing device which is assigned to a service provider, wherein the confidential data are assigned to a personalized data-processing operation in the first data-processing device; - storing the confidential data in a storage device, from which at least the first data-processing device is capable of retrieving data; - providing secret data which represent a secret agreed upon between the service provider and a person to whom the personalized data-processing operation is assigned, in the first data-processing device; - transmitting message data from the first data-processing device to a second data-processing device, which is assigned to a message service provider and is configured to transmit received message data to one or more landline telephones in a network of landline telephones, wherein the message data comprise the following: - the confidential data, - the secret data and - receiver data which indicate a landline telephone in the network of landline telephones as receiving device; - the confidential data, - the secret data and - receiver data which indicate a landline telephone in the network of landline telephones as receiving device; - querying the secret via the landline telephone in response to an evaluation of the message data by the second data-processing device; - receiving user input data in the landline telephone via an input device of the landline telephone; - transmitting the user input data from the landline telephone to the second data-processing device; - evaluating the user input data by the second data-processing device; - transmitting the confidential data from the second data processing device to the landline telephone, if it is determined during evaluation that the user input data correctly indicate the secret agreed upon between the service provider and the individual; and - outputting the confidential data via an output device of the landline telephone.