A method for authentication of a secure transaction to be conducted between a secure transaction host and a transacting user, the method to be carried out at an authentication service provider and comprising the steps of: receiving an authentication request from the secure transaction host; receiving a digital identifier containing a hardware identifier from a mobile communications device associated with the transacting user whereby the mobile communications device may be uniquely identified, the digital identifier having been created, without user intervention, by an authentication application installed on the mobile communications device as a function of the hardware identifier and at least a random number created by the authentication application such that the digital identifier cannot be re-created without the mobile communications device of the user and thereby establishing a one-to-one association between the digital identifier and the mobile communications device of the user, the digital identifier being stored in a secure storage location on the mobile communications device from where it is retrievable only by authorized applications including the authentication application; comparing the digital identifier with a list of digital identifiers associated with mobile communications devices of pre-enrolled users stored on a database associated with the authentication service provider; if the received digital identifier corresponds to a digital identifier stored on the database, allowing a secure communications link to be established between the mobile communications device of the transacting user and the authentication service provider, the secure communications link being initiated from the authentication application on the mobile communications device; transmitting a transaction confirmation request to the mobile communications device of the transacting user over the secure communications link, the request requiring the user to confirm or deny its intended performance of the secure transaction; receiving a confirmation or denial result from the mobile communications device; in response to a confirmation result, transmitting a positive authentication result to the secure transaction host; and in response to a denial result, transmitting a negative authentication result to the secure transaction host. receiving an authentication request from the secure transaction host; receiving a digital identifier containing a hardware identifier from a mobile communications device associated with the transacting user whereby the mobile communications device may be uniquely identified, the digital identifier having been created, without user intervention, by an authentication application installed on the mobile communications device as a function of the hardware identifier and at least a random number created by the authentication application such that the digital identifier cannot be re-created without the mobile communications device of the user and thereby establishing a one-to-one association between the digital identifier and the mobile communications device of the user, the digital identifier being stored in a secure storage location on the mobile communications device from where it is retrievable only by authorized applications including the authentication application; comparing the digital identifier with a list of digital identifiers associated with mobile communications devices of pre-enrolled users stored on a database associated with the authentication service provider; if the received digital identifier corresponds to a digital identifier stored on the database, allowing a secure communications link to be established between the mobile communications device of the transacting user and the authentication service provider, the secure communications link being initiated from the authentication application on the mobile communications device; transmitting a transaction confirmation request to the mobile communications device of the transacting user over the secure communications link, the request requiring the user to confirm or deny its intended performance of the secure transaction; receiving a confirmation or denial result from the mobile communications device; in response to a confirmation result, transmitting a positive authentication result to the secure transaction host; and in response to a denial result, transmitting a negative authentication result to the secure transaction host.