Abstract: A method is proposed for acquiring a service sold over a data network (20) against presentation of a transaction medium (2). The service is ordered by a user (1) by a user end system (10) from a service provider (40). The latter calls in a clearing center (30) which enters into a data exchange with the transaction medium (2) to call for therefrom a necessary contribution in the form of certain data assumed for acquisition of the service. The ordering process and the data exchange with the transaction medium (2) for calling for the contribution are linked via an identifier (KM) associated with the transaction medium (2), the identifier being determined by the user end system (10) and used to secure the ordering process and the call for the contribution.

Abstract: A method is proposed for acquiring a service sold over a data network (20) against presentation of a transaction medium (2). The service is ordered by a user (1) by a user end system (10) from a service provider (40). The latter calls in a clearing center (30) which enters into a data exchange with the transaction medium (2) to call for therefrom a necessary contribution in the form of certain data assumed for acquisition of the service. The ordering process and the data exchange with the transaction medium (2) for calling for the contribution are linked via an identifier (KM) associated with the transaction medium (2), the identifier being determined by the user end system (10) and used to secure the ordering process and the call for the contribution.

Abstract: A method is described for protecting a transaction over a computer network by which a one-time transaction password is transmitted to a service user and transmitted by the service user to a service provider over the computer network to confirm the transaction. The transaction password is transmitted over a mobile network to the service user's mobile communication terminal.

Abstract: A method for producing a filter includes the steps of providing a blank of etchable semiconductor material having a first side and a second side and affixing a holding element to the blank. The holding element is chemically resistant to an etching solution. A current source is connected to the blank and at least one of the first and second sides of the blank is illuminated with light. The holding element and the blank are immersed in the etching solution until the first side of the blank is wetted so that the first side is etched electrochemically. The holding element is affixed to the blank such that contact areas between the holding element and the blank remain free of the etching solution.