A method of authenticating a user of a mobile communication device, comprising: directing, by a first application or program executing on the mobile communication device, transmission, from the mobile communication device to a security server, of a request for authentication of the user in connection with either (i) the user logging into or (ii) the user entering into a transaction with a network site; receiving, by a second application or program executing on the mobile communication device, the request for authentication from the security server; directing, by the second application or program, presentation by the mobile communication device of the received request for authentication to the user; receiving, by the second application or program, a user input to the mobile communication device indicating that the requested authentication should proceed; directing, by the second application or program in response to the received user input, transmission, from the mobile communication device to the security server, of an indication that the requested authorization should proceed; receiving, by the second application or program from the security server, a personal identification number, in response to the transmission of the indication that the requested authorization should proceed; storing, by the second application or program, the received PIN in a public data store within the mobile communications device; retrieving, by the first application or program, the stored PIN from the public data store; and directing, by the first application or program, transmission, from the mobile communications device to the network site, of the retrieved PIN, to authenticate the user or transaction to the network site; wherein preferably the mobile communication device is a smart phone. directing, by a first application or program executing on the mobile communication device, transmission, from the mobile communication device to a security server, of a request for authentication of the user in connection with either (i) the user logging into or (ii) the user entering into a transaction with a network site; receiving, by a second application or program executing on the mobile communication device, the request for authentication from the security server; directing, by the second application or program, presentation by the mobile communication device of the received request for authentication to the user; receiving, by the second application or program, a user input to the mobile communication device indicating that the requested authentication should proceed; directing, by the second application or program in response to the received user input, transmission, from the mobile communication device to the security server, of an indication that the requested authorization should proceed; receiving, by the second application or program from the security server, a personal identification number, in response to the transmission of the indication that the requested authorization should proceed; storing, by the second application or program, the received PIN in a public data store within the mobile communications device; retrieving, by the first application or program, the stored PIN from the public data store; and directing, by the first application or program, transmission, from the mobile communications device to the network site, of the retrieved PIN, to authenticate the user or transaction to the network site; wherein preferably the mobile communication device is a smart phone.