Method with which a mobile user can confirm a transaction with a service provider, in which:an offer of said service provider is reproduced with the mobile device of said mobile user,said mobile user selects said offer with input means of his mobile device,a transaction confirmation is automatically forwarded from said mobile device to an authentication server, a plurality of transactions between different mobile users and different service providers being stored in said authentication server,and said service provider retrieves said confirmation from said authentication server.