The system and method performing secure online-transactions based on challenge/response procedures executed by a terminal of at least one customer and by a terminal of a service provider, such as a bank, which terminals are connected to a network, preferably the Internet. The inventive method including: capturing biometric elements, such as audio and video samples or related biometric data, from the customer during an enrollment procedure and storing the biometric elements in a database, which is accessible by the service provider's terminal; executing synchronized challenge procedures for each transaction in order to produce identical challenges based on current transaction data; capturing biometric data from the customer's response to the challenge with the customer's terminal; delivering transaction data together with the biometric data of the customer's response to the service provider's terminal; retrieving and assembling biometric elements according to the challenge in order to assemble response in the service provider's terminal; and comparing the biometric data of customer's response with the data of the assembled response and performing the requested transaction in the event that the data of the responses match.