Igarcom to implemented a service of backup online, which allows him to make backups from a remote writing-desk to our servants who are located in center of data of banesto. The copies are realized of difeencial form with FastBIT technology that allows the shipment of the bytes that they change of each registry, allowing a fast transmission still in case of a width gives small band. The security is guaranteed by means of the coding of the origin of the information before being sent. A private key and a Bolwfish algorithm of 448 bits or AES are used