1. A method for increasing the security of network-based transactions conducted on mobile communications devices, said method comprising: requesting to conduct a network-based transaction from a mobile communications device requiring access to resources controlled by a service provider system; determining authentication data to be captured based on the requested transaction at an authentication system, including the authentication data to be captured in a capture request message, and transmitting the capture request message to the mobile communications device; determining whether authentication data to be captured, that is included in the capture request message, agrees with authentication data anticipated for the requested transaction; capturing authentication data from a user of the mobile communications device in accordance with the capture request message when the authentication data to be captured in the capture request message agrees with the anticipated authentication data; transmitting the captured authentication data to the authentication system; comparing the received authentication data against enrollment authentication data of the user and successfully authenticating the user when the received and enrollment authentication data match; and conducting the requested transaction after successfully authenticating the user.