First off, true confession: I'm not a technology expert. I can tell you, though, that they come from far and wide and that we invest tens of millions of dollars every year in VisaNet protection.
That protection ensures that the data, as it's travelling through the network, is not able to be hacked and that the fraudsters who are attacking with a really wide variety of attacks are thwarted before they get too far.
I would be very happy to connect you with someone who's more qualified to provide you with more technical detail on that.