Method for securing a transaction between a mobile terminal of a user and a server of a service provider by way of a platform connected to the mobile terminal via an access platform for accessing the Internet network of a mobile network of an operator, to the server of the service provider and to a transaction execution system, the method comprising the following steps: - generation by said access platform for accessing the Internet network of the mobile network of an item of alias data associated with a user identifier by means of which the mobile terminal is identified by the mobile network of the operator in a database specific to the operator, the platform having no knowledge of said user identifier; - storage by the platform of a correspondence between a user identification code at the transaction execution system and the alias data, - establishment of a connection between the mobile terminal and the platform by way of the access platform for accessing the Internet network of the mobile network to the Internet network of the mobile network, - reception by the platform from the access platform for accessing the Internet network of the mobile network of the alias data during the establishment of the connection between the mobile terminal and the platform, - linking, by way of the platform and via the access platform for accessing the Internet network of the mobile network to the Internet network of the mobile network, the mobile terminal of the user with the server of the service provider, said alias data being used by said server of the service provider to identify the mobile terminal, the access platform replacing the user identifier with the alias data when the mobile terminal communicates with the server or the platform and identifying, by means of the user identifier associated with the alias data, the mobile terminal when the server or the platform communicates with the terminal, - reception by the platform of transaction data representative of a transaction to be executed between the user of the mobile terminal and said service provider, - transmission by the platform to the transaction execution system of an order to execute the transaction comprising said user identification code and an identification code of the service provider at the transaction execution system such that the transaction execution system implements said transaction. - generation by said access platform for accessing the Internet network of the mobile network of an item of alias data associated with a user identifier by means of which the mobile terminal is identified by the mobile network of the operator in a database specific to the operator, the platform having no knowledge of said user identifier; - storage by the platform of a correspondence between a user identification code at the transaction execution system and the alias data, - establishment of a connection between the mobile terminal and the platform by way of the access platform for accessing the Internet network of the mobile network to the Internet network of the mobile network, - reception by the platform from the access platform for accessing the Internet network of the mobile network of the alias data during the establishment of the connection between the mobile terminal and the platform, - linking, by way of the platform and via the access platform for accessing the Internet network of the mobile network to the Internet network of the mobile network, the mobile terminal of the user with the server of the service provider, said alias data being used by said server of the service provider to identify the mobile terminal, the access platform replacing the user identifier with the alias data when the mobile terminal communicates with the server or the platform and identifying, by means of the user identifier associated with the alias data, the mobile terminal when the server or the platform communicates with the terminal, - reception by the platform of transaction data representative of a transaction to be executed between the user of the mobile terminal and said service provider, - transmission by the platform to the transaction execution system of an order to execute the transaction comprising said user identification code and an identification code of the service provider at the transaction execution system such that the transaction execution system implements said transaction.