A method for verifying, in controlled manner and on the basis of at least one biometric characteristic, the assumed identity of a calling and/or called subscriber that is connected via a communication terminal to a telecommunications network, for connecting the subscriber to a communication system which supports a number of at least two communication services requiring authentication and having different security requirements; wherein after establishing a communication connection between the subscriber and a verification device connected to the telecommunications network, a determined identity identifier and the subscriber are associated with each other in order to identify the subscriber, a request to use at least one of the communication services requiring authentication is transmitted to the verification device, at least one biometric sample of the subscriber is acquired and a biometric characteristic structure is detected from the biometric sample; and wherein when performing subscriber authentication for the requested communication service, a biometric imprint (20a, 20b, 20c) initially associated with and stored for the identity identifier for subscriber authentication of the number of communication services requiring authentication is compared, as a reference imprint, with at least one characteristic of the detected biometric characteristic structure; if a first threshold value (11a, 11b,..., 11e) is reached, the identification of the calling subscriber is verified for the requested communication service in response to the comparison result, and the calling subscriber is connected to the communication system supporting said requested communication service; and if a second threshold (16, 11a, 11b,..., 11e) is reached, an adapted biometric imprint is calculated in response to the comparison result using the detected biometric characteristic structure (18, 19, 26, 27) and is associated with and stored for the identity identifier for subscriber authentication for the number of communication services requiring authentication instead of the biometric imprint used as the reference imprint; characterized in that a) the second threshold value is consistent for the number of the at least two communication services requiring authentication; and/or wherein if the identity of the subscriber has been verified, the obtained comparison value is made available to the communication system, the obtained comparison value is compared, by the communication system, with a second threshold value which is consistent for the number of the at least two communication services requiring authentication and/or corresponds to the first threshold value of the highest security level, and in response to the comparison result, an adaptation of the biometric imprint used as the reference imprint, which has possibly already been made by the verification device, is undone. a) the second threshold value is consistent for the number of the at least two communication services requiring authentication; and/or wherein if the identity of the subscriber has been verified, the obtained comparison value is made available to the communication system, the obtained comparison value is compared, by the communication system, with a second threshold value which is consistent for the number of the at least two communication services requiring authentication and/or corresponds to the first threshold value of the highest security level, and in response to the comparison result, an adaptation of the biometric imprint used as the reference imprint, which has possibly already been made by the verification device, is undone.