A method is provided for conducting a financial transaction by a purchaser
with a merchant having an acquirer bank, over a communications network.
The method includes the steps of sending a first authorization request
using a pseudo account number associated with a real account number to a
service provider which forwards a second authorization request to the
issuer using the real account number and preferably a pseudo acquirer
code associated with the service provider such that the response to the
second request is based on the real account number and sent back to the
service provider who preferably forwards a response to the first request
preferably to the "real" acquirer. A message authentication code is
further provided which includes transaction data, and where the
authorization request is formatted as a standard payment card track
having one or more fields including a discretionary field in which the
message authentication code is placed.