A method is provided for authenticating debit card transactions engaged in by a cardholder on a communications network. The method includes: a) establishing a connection over the network with a client being used by the cardholder to engage in a transaction on the network; b) providing over the connection to the client a web page containing a keypad (22) having a plurality of buttons (24) that collectively define a geometry of the keypad (22), the keypad (22) being employed by the cardholder to enter a PIN via selection of the buttons (24) with a pointing device of the client; c) obtaining over the connection the PIN enter by the cardholder; d) determining if the obtained PIN is correct for a debit card being used by the cardholder to engage in the transaction; e) repeating step a) through d) for each transaction the cardholder engages in on the network; and, f) with respect to two transactions engaged in by the cardholder, changing at least one of a location of the keypad (22) on the web page, the geometry of the keypad (22), a size of the buttons (24) and a spacing between neighboring buttons (24).