Page 106 of Chain Reaction

“But?”

“My John reasoned a hacker wouldn’t want to be identified as a hacker, so he would steal a document and then make it physical by printing it out and photographing it, so that everyone would go look for thieves or traitors, not hackers. Just like John the boss actually had. My John wondered if the Vietnam thing was someone’s trial run. It looked old, but you can do anything with a photograph in a computer.”

Julia took a drink of water. The baby let go of Reacher’s knuckle, and then immediately wanted it back again. Reacher gave her the tip of his pinkie instead. He didn’t want to damage her tender ligaments.

“Then what happened?” he asked.

“Amanda was born,” Julia said. “John didn’t do much at work for a couple of weeks. Then he got back to it. He suddenly got interested in the geographic routing of data packets.”

“Which are what exactly?”

“Sending a document over the internet is not the same as putting it in an envelope and taking it to the post office. It’s like tearing it into a hundred pieces and putting them in a hundred envelopes and taking them to a hundred post offices, each of which will mail its envelope by a different route. They’ll go all over the world, crazy directions, crisscrossing, one split-second decision after another, depending on where the congestion looks like easing up a millisecond from now. Then they all arrive at the destination and someone tapes the document back together again, with all the pages in the correct order.”

“Weird, but OK,” Reacher said. “Whatever.”

“John created a hundred million test documents with trackable code in the header information. I helped with that too. They were designed to create about ten billion data packets. John watched where they went. Not literally, you understand. They washed through the global network at about a billion packets per second. We wrote code to reconstruct the physical geography and present it as a schematic. Like a subway map. It took forever. Amanda was three weeks old when we started. She could sit up by herself when we finished. And then we had to do it all again.”

“Why?”

“It was a huge sample size over a very long period of time, in electronic terms, so you would expect the locations to average out to completely random. The map should have shown millions of dots with no obvious patterns or clusters. And it did. He ran some math on a sample section, and the distribution proved to be insignificantly different than pure chance. All good. Except that when he looked at the schematic on the screen, he thought one of the dots was brighter than the rest. He assumed his video driver was introducing an error, or his screen was shot. He tried it from home, on a laptop, with a different driver and a different screen. That was when I first saw it. It was still way brighter.”

“What did it mean?”

“Nothing we could think of made sense. We did some complicated math and zoomed in tight, and we kind of reconstructed what must be there from the numbers. It looked like a pretty normal five-building cluster. Five data centers close together. Usually the zoning limit, because of power and water. You see them everywhere. But the numbers were weird. Four of the data centers were getting their own fair share of random hits as expected. But all of those hits were also showing up inside the fifth data center. Which was also getting its own fair share of random hits as expected. It was processing five times more data than pure chance said it should. Therefore the cluster as a whole was processing one-point-eight times more than chance said it should. The math in our software represented that as a dot one-point-eight times brighter than the others.”

Turner asked, “Where was this cluster?”

“We couldn’t tell,” Julia said. “That was why we had to rewrite the software. A subway map is not geographically accurate. We needed an actual map. Which was a lot of effort. To save time he would leave the program running all night at work. One morning it was ready. He called me and said the cluster was in Colorado and he was heading out there. That was our last conversation. The last time we ever spoke. I told him to have a good trip, and he told me to take care of myself.”

“I’m so sorry,” Turner said.

Julia was quiet a moment.

“I’ve got Amanda,” she said. “Half of her is him. He lives on, a little bit.”

Reacher said, “Did you have an opinion about how that one particular center was getting five times more data than it should?”

“A thing called a switcher decides where any individual data packet goes next. As a million to one theoretical possibility, I suppose you could imagine a switcher malfunction causing it. Or as a billion to one theoretical possibility you could imagine a hack having the same effect. But logic says it can’t be either of those things.”

“Why not?”

“Because a data packet is an actual thing. It can’t be in two places at once. It can’t be in both data center one and data center two at the same time. Or three and four, or whatever. In the normal course of events a data packet can get lost or damaged somewhere in the network, in which case the next switcher would call back upstream and order a duplicate to replace it. That happens. But it’s literally impossible to imagine a switcher malfunction that would route the packets incorrectly while simultaneously ordering duplicates, because somehow it knows ahead of time it will need them, simply to fulfill its own invalid routing decision. That would be more than a malfunction. It would be a full-on nervous breakdown.”

“Could a hack do that?”

“In principle a hack could do anything, but we know that isn’t happening.”

“How do you know?”

“The duplicate packets would have the same tracker in the header information. We would see them come in. First the original, then the duplicate. But we didn’t see that. Only one of each packet came in, yet four out of five of them showed up in two places at once.”

“What could explain that?”

“Nothing,” Julia said.

—

They left Julia and Amanda in their living room and rode back down to the street. Turner reclaimed her car. Reacher gave her the key and got in on the passenger side. He moved the seat back to where he needed it. She got in on the driver’s side and moved the seat up a corresponding amount. She started the motor to run the air. Reacher gave back her pistol. She put it in the glove box.