1. Electronic system for authenticating a user of an electronic service, said system preferably comprising at least one server apparatus, the system being configured to store, for a number of users, a plurality of personal voiceprints each of which being linked with a dedicated visual, audiovisual or audio cue, for challenge-response authentication of the users, wherein the cues are user-selected, user-provided or user-created, pick, upon receipt of an authentication request associated with a claim of an identity of an existing user of said number of users, a subset of cues for which there are voiceprints of the existing user stored, and provide the cues for representation to the user as a challenge, receive sound data indicative of voice responses uttered by the user to the represented cues, said voice responses represented by the sound data being captured simultaneously utilizing both an air microphone and contact microphone preferably integrated in a common microphone apparatus, determine on the basis of the sound data, the represented cues and voiceprints linked therewith and the existing user, whether the response has been uttered by the existing user of said number of users, wherein the sound data indicative of the voice responses uttered to the represented cues are preferably matched as concatenated against a concatenated voiceprint established based on the voiceprints linked with the represented cues and the existing user, and provided that this seems to be the case, elevate the authentication status of the user as the existing user, preferably regarding at least the current communication session.