A system and a method is shown for conducting electronic commerce. The system includes a mobile station (10) containing a user interface (15) and an application (27A), which could cooperate with a user authentication module (13A); and a computer (1) coupled to a data communications network (2). The computer includes a browser (1A) for contacting a site, such as a commerce related site, and a browser plug-in module (1B) and/or a browser extension. The browser and plug-in (or extension) cooperate to detect a presence of a received message that requires a response from the user, such as an authentication of the user, or a digital signature, or a payment request, etc. The computer also includes an interface (1C, 1D, 1E) for sending a message from the computer to the mobile station over a bidirectional link (3). The mobile station application is responsive to the receipt of the message from the computer for generating a user response message and for passing the generated user response message to the computer over the link. The computer is responsive to a receipt of the user response message for sending user response information to the site using the browser. The mobile station, or the computer, operates to prompt the user to enter a personal identification number, and the entered PIN is compared to a PIN stored in the mobile station. The link may be implemented using Bluetooth technology.