Method and system for validating a transaction, transaction terminal and corresponding program.

The method involves decoding a validation code (24) generated and displayed by a transactional terminal, where the validation code is entered by a user in a validation message. The validation code is transmitted by a mobile device of the user to an entity of a mobile telecommunication network to which the mobile device and the terminal are connected. Transaction is validated when the identified terminal is found in a covering zone of an identified base station to which the mobile device is connected. Independent claims are also included for the following: (1) a system for validating a transaction on a transactional terminal (2) a transactional terminal comprising a generating unit for generating a validation code (3) a computer program product comprising a set of instructions for implementing a method for validating a transaction on a transactional terminal.