A means of transaction authorization using a vocalized challenge response. The method comprises the steps of transaction authorization server (30), receiving from a computerized transaction system (20), transaction request data responsive to a user (1) having initiated (S20) a transaction via the transaction system; generating (S50) a single use, one-time challenge, vocalized by voice synthesis and call a computerized electronic device (10, 10a, 10b) of the user such as a smartphone or phablet, using an endpoint identifier linked to the user (such as a mobile phone number), the latter enrolled (S10) at the server, to vocally communicate the vocalized challenge to the user; and communicating (S70) with the transaction system to validate response data sent by the user to the server and/or the transaction system for validation, to authorize (S80) the transaction. The invention provides an alternate method of authorization from known methods of utilizing mobile Transaction Authentication Numbers (mTAN) currently issued via Standard Message Service (SMS) text messages. The preferred embodiment is for use in financial transactions being executed on a smartphone or like, where the voice response, uses two separate channels for execution and authentication making an attack significantly more difficult.
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