oks' offices in the Flatiron Building and everytime I dro in to meet with the Tor people, I always sneak away to Booksof Wonder to peruse their stock of new, used and

them sort through the haystack to find aneedle.""But by taking in all that data from the transit system, they're creatingthe haystack," I said. "That's a gigantic mountain of data and there's al-most nothing worth looking at there, from the police's point of view. It'sa total waste."95"I understand that you don't like that this system caused you some in-convenience, Marcus. But you of all people should appreciate the gravityof the situation. There was no harm done, was there? They even gaveyou a ride home."They threatened to send me to jail, I thought, but I could see there was nopoint in saying it."Besides, you still haven't told us where the blazing hells you've beento create such an unusual traffic pattern."That brought me up short."I thought you relied on my judgment, that you didn't want to spy onme." He'd said this often enough. "Do you really want me to account forevery trip I've ever taken?"I hooked up my Xbox as soon as I got to my room. I'd bolted the pro-jector to the ceiling so that it could shine on the wall over my bed (I'dhad to take down my awesome mural of punk rock handbills I'd takendown off telephone poles and glued to big sheets of white paper).I powered up the Xbox and watched as it came onto the screen. I wasgoing to email Van and Jolu to tell them about the hassles with the cops,but as I put my fingers to the keyboard, I stopped again.A feeling crept over me, one not unlike the feeling I'd had when I real-ized that they'd turned poor old Salmagundi into a traitor. This time, itwas the feeling that my beloved Xnet might be broadcasting the locationof every one of its users to the DHS.It was what Dad had said: You ask the computer to create a profile of anaverage record in a database and then ask it to find out which records in thedatabase are furthest away from average.The Xnet was secure because its users weren't directly connected to theInternet. They hopped from Xbox to Xbox until they found one that wasconnected to the Internet, then they injected their material as unde-cipherable, encrypted data. No one could tell which of the Internet'spackets were Xnet and which ones were just plain old banking and e-commerce and other encrypted communication. You couldn't find outwho was tying the Xnet, let alone who was using the Xnet.But what about Dad's "Bayesian statistics?" I'd played with Bayesianmath before. Darryl and I once tried to write our own better spam filterand when you filter spam, you need Bayesian math. Thomas Bayes wasan 18th century British mathematician that no one care about until a96couple hundred years after he died, when computer scientists realizedthat his technique for statistically analyzing mountains of data would besuper-useful for the modern world's info-Himalayas.Here's some of how Bayesian stats work. Say you've got a bunch ofspam. You take every word that's in the spam and count how manytimes it appears. This is called a "word frequency histogram" and it tellsyou what the probability is that any bag of words is likely to be spam.Now, take a ton of email that's not spam — in the biz, they call that"ham" — and do the same.Wait until a new email arrives and count the words that appear in it.Then use the word-frequency histogram in the candidate message to cal-culate the probability that it belongs in the "spam" pile or the "ham" pile.If it turns out to be spam, you adjust the "spam" histogram accordingly.There are lots of ways to refine the technique — looking at words inpairs, throwing away old data — but this is how it works at core. It's oneof those great, simple ideas that seems obvious after you hear about it.It's got lots of applications — you can ask a computer to count thelines in a picture and see if it's more like a "dog" line-frequency histo-gram or a "cat" line-frequency histogram. It can find porn, bank fraud,and flamewars. Useful stuff.And it was bad news for the Xnet. Say you had the whole Internetwiretapped — which, of course, the DHS has. You can't tell who'spassing Xnet packets by looking at the contents of those packets, thanksto crypto.What you can do is find out who is sending way, way more encryptedtraffic out than everyone else. For a normal Internet surfer, a session on-line is probably about 95 percent cleartext, five percent ciphertext. Ifsomeone is sending out 95 percent ciphertext, maybe you could dispatchthe computer-savvy equivalents of Booger and Zit to ask them if they'reterrorist drug-dealer Xnet users.This happens all the time in China. Some smart dissident will get theidea of getting around the Great Firewall of China, which is used to cen-sor the whole country's Internet connection, by using an encrypted con-nection to a computer in some other country. Now, the Party there can'ttell what the dissident is surfing: maybe it's porn, or bomb-making in-structions, or dirty letters from his girlfriend in the Philippines, or polit-ical material, or good news about Scientology. They don't have to know.All they have to know is that this guy gets way more encrypted trafficthan his neighbors. At that point, they send him to a forced labor camp97just to set an example so that everyone can see what happens to smart-asses.So far, I was willing to bet that the Xnet was under the DHS's radar,but it wouldn't be the case forever. And after tonight, I wasn't sure that Iwas in any better shape than a Chinese dissident. I was putting all thepeople who signed onto the Xnet in jeopardy. The law didn't care if youwere actually doing anything bad; they were willing to put you underthe microscope just for being statistically abnormal. And I couldn't evenstop it — now that the Xnet was running, it had a life of its own.I was going to have to fix it some other way.I wished I could talk to Jolu about this. He worked at an Internet Ser-vice Provider called Pigspleen Net that had hired him when he wastwelve, and he knew way more about the net than I did. If anyone knewhow to keep our butts out of jail, it would be him.Luckily, Van and Jolu and I were planning to meet for coffee the nextnight at our favorite place in the Mission after school. Officially, it wasour weekly Harajuku Fun Madness team meeting, but with the gamecanceled and Darryl gone, it was pretty much just a weekly weep-fest,supplemented by about six phone-calls and IMs a day that went, "Areyou OK? Did it really happen?" It would be good to have something elseto talk about."You're out of your mind," Vanessa said. "Are you actually, totally,really, for-real crazy or what?"She had shown up in her girl's school uniform because she'd beenstuck going the long way home, all the way down to the San Mateobridge then back up into the city, on a shuttle-bus service that her schoolwas operating. She hated being seen in public in her gear, which wastotally Sailor Moon — a pleated skirt and a tunic and knee-socks. She'dbeen in a bad mood ever since she turned up at the cafe, which was fullof older, cooler, mopey emo art students who snickered into their latteswhen she turned up."What do you want me to do, Van?" I said. I was getting exasperatedmyself. School was unbearable now that the game wasn't on, now thatDarryl was missing. All day long, in my classes, I consoled myself withthe thought of seeing my team, what was left of it. Now we werefighting.98"I want you to stop putting yourself at risk, M1k3y." The hairs on theback of my neck stood up. Sure, we always used our team handles atteam meetings, but now that my handle was also associated with myXnet use, it scared me to hear it said aloud in a public place."Don't use that name in public anymore," I snapped.Van shook her head. "That's just what I'm taking about. You could endup going to jail for this, Marcus, and not just you. Lots of people. Afterwhat happened to Darryl —""I'm doing this for Darryl!" Art students swiveled to look at us and Ilowered my voice. "I'm doing this because the alternative is to let themget away with it all.""You think you're going to stop them? You're out of your mind.They're the government.""It's still our country," I said. "We still have the right to do this."Van looked like she was going to cry. She took a couple of deepbreaths and stood up. "I can't do it, I'm sorry. I can't watch you do this.It's like watching a car-wreck in slow motion. You're going to destroyyourself, and I love you too much to watch it happen."She bent down and gave me a fierce hug and a hard kiss on the cheekthat caught the edge of my mouth. "Take care of yourself, Marcus," shesaid. My mouth burned where her lips had pressed it. She gave Jolu thesame treatment, but square on the cheek. Then she left.Jolu and I stared at each other after she'd gone.I put my face in my hands. "Dammit," I said, finally.Jolu patted me on the back and ordered me another latte. "It'll be OK,"