A method for performing secure transactions, such as credit card purchases, using two or more non-secure networks (such as the Internet and the public telephone system) in such a way that security is insured. A person wishing to initiate a secure transaction sends a message over one of the non-secure networks to a computer. That computer automatically uses the second non-secure network to contact the person back to verify the transaction. The call-back mechanism employs a method to authenticate the identity or authority of the person initiating the transaction. No single wire-tapping or network snooping device sees the entire transaction. No single database contains the entire set of information.