Abstract: A memory support for a program for controlling a method for securely conducting commercial and banking transactions in a telecommunications and computer network with electronic commerce sites and credit institutions, portable, of the laser-read type, functioning as a payment card to be inserted in a related reader on a users computer, containing a stored software that includes: a user data certificate in digital format able to allow banking operations, once it is duly activated by means of a secret code of a user holding said memory support as holder of an account with a credit institution, and a program able to communicate with other programs residing in computers or servers at said electronic commerce sites and credit institutions interested in said commercial and banking operations through any computer provided with common programs for connecting to the telecommunications and computer network.