The present invention relates to a method of enabling a computer network transaction for a product being purchased by a buyer from a seller, comprising the steps of generating a once-only transaction identification means associated with the transaction, providing the transaction identification means to a transaction acquirer, together with a buyer identification means which identifies the buyer to the transaction acquirer, and providing the once-only identification means to the seller, whereby the seller may provide the transaction identification means to the transaction acquirer and the transaction acquirer can match the transaction identification means received from the seller with the transaction identification means they have been provided with and, if they match, can enable settlement of the transaction.