“What does that mean?” This time it was Agent Carter that was puzzled.
Lisa smiled. This is the question she was waiting for. “It means that the hacker is profiting from the flow of money. We are certain that somewhere in the tangle of bogus EFT’s, there is a bank account owned by the hacker and that he is earning interest on continuous 24-hour loans. By routing large amounts money through his bank account, the hacker collects interest. By making sure that he returns the money quickly, and by borrowing only a small amount of money from any individual account, the hacker ensures that nobody misses their money. By using error-correcting EFT’s, the hacker avoids leaving any evidence on customers’ monthly statements.”
Lisa looked around the room to make sure that her point had sunk in. It had. Jonny whistled softly. Templemeyer nodded slowly to himself. Agnes was not as impressed.
“Surely it is an easy matter to determine which bank account is the focal point for all of the bogus EFT’s,” she snappped. “We can put a stop to this soon enough.”
“It isn’t that easy,” said Lisa. “The hacker is quite clever and has obscured his activities by generating thousands of decoys. It is hard enough to recognize a bogus EFT — because they are perfect forgeries — without the added complication of chasing down false leads caused by decoys. It simply takes too long to track down every bogus EFT and trace the flow of counterfeit money.”
“That problem is easily solved,” Agnes interrupted. “I can assign more people to the case.”
Lisa shook her head. “There are too many. Tens of thousands of bogus EFT’s daily, only a small fraction of which will lead to the hacker. Some of the EFT’s are for only a few pennies. In many cases a single deposit is seperated into several withdrawals. For example a deposit of $500 might be balanced by five withdrawals of $100. Now tracing one route through the banking network becomes a matter of tracing five routes. A few more splits like that and very soon we find ourselves tracing hundreds of routes just to see what happens to the original $500. And it isn’t like there is an obvious place to start looking. In that last example, the original $500 EFT is part of a larger loop. Keep in mind that very rarely is money stolen… only borrowed.”
Jonny leaned back in his chair and twirled his pencil in his hand. He fumbled it. As he leaned forward to pick it up he cleared his throat to speak. He directed his comments toward me.
“Can’t you write a program to track the money throught the system?”
“We have,” Lisa said before I could respond. “But the shear number of paths the money takes is too much even for a computer to track. Path enumeration in a graph is an NP-complete problem.”
She was met with blank stares. Struggling to find the right words, she pressed on. “We have written a program to trace the flow of illicit money through the system, just as you suggest, but it is unlikely that we will ever uncover anything. The millwright is smart enough to use lots of decoys. He must be using a computer himself to generate the decoys and to route them through the system so that they move money in long convoluted circles. The money is divided and re-combined in complex patterns. Our program might never find the millrace no matter how long we let it run.”
The amused twinkle returned to Templemeyer’s eyes despite the gravity of the situation described by Lisa. “The millwright?” he asked. “Did you say millwright Ms. Cryer?”
Lisa smiled sheepishly and shrugged her shoulders. She glanced at me, embarrased. I straightened up and came to her support.
“It is the name we have given the hacker,” I explained. “The flow of small amounts of counterfeit money throughout a complex network, with profits derived from the carefully engineered redirection of the flow, conjures up the image of a water mill. The bank accounts where interest payments are collected by the hacker would be analogous to the water wheel. A millwright is a person that runs a mill. A millrace is the chute that directs water over the wheel.
“We need to find the millrace. Find that, and we can find the water wheel — the bank account owned by the millwright.”
“I see,” Templemeyer said with with some amusement. “You people have been investigating this matter for some time I suppose. You seem to have a good understanding of the nature of the crimes. How do you propose we go about solving this case?” Then, with a light chuckle, he rephrased his question. “How do we find the millrace and thereby expose the millwright?”