“That’s not what I meant. I didn’t mean you should get everyone arrested. If you want to protest, join the protest movement. Do something positive. Didn’t you learn anything from Darryl? Anything?”
“You’re damned right I did,” I said, losing my cool. “I learned that they can’t be trusted. That if you’re not fighting them, you’re helping them. That they’ll turn the country into a prison if we let them. What did you learn, Van? To be scared all the time, to sit tight and keep your head down and hope you don’t get noticed? You think it’s going to get better? If we don’t do anything, this is as good as it’s going to get. It will only get worse and worse from now on. You want to help Darryl? Help me bring them down!”
There it was again. My vow. Not to get Darryl free, but to bring down the entire DHS. That was crazy, even I knew it. But it was what I planned to do. No question about it.
Van shoved me hard with both hands. She was strong from school athletics — fencing, lacrosse, field hockey, all the girls-school sports — and I ended up on my ass on the disgusting San Francisco sidewalk. She took off and I didn’t follow.
> The important thing about security systems isn’t how they work, it’s how they fail.
That was the first line of my first blog post on Open Revolt, my Xnet site. I was writing as M1k3y, and I was ready to go to war.
> Maybe all the automatic screening is supposed to catch terrorists. Maybe it will catch a terrorist sooner or later. The problem is that it catches us too, even though we’re not doing anything wrong.
> The more people it catches, the more brittle it gets. If it catches too many people, it dies.
> Get the idea?
I pasted in my HOWTO for building an arphid cloner, and some tips for getting close enough to people to read and write their tags. I put my own cloner in the pocket of my vintage black leather motocross jacket with the armored pockets and left for school. I managed to clone six tags between home and Chavez High.
It was war they wanted. It was war they’d get.
If you ever decide to do something as stupid as build an automatic terrorism detector, here’s a math lesson you need to learn first. It’s called “the paradox of the false positive,” and it’s a doozy.
Say you have a new disease, called Super-AIDS. Only one in a million people gets Super-AIDS. You develop a test for Super-AIDS that’s 99 percent accurate. I mean, 99 percent of the time, it gives the correct result — true if the subject is infected, and false if the subject is healthy. You give the test to a million people.
One in a million people have Super-AIDS. One in a hundred people that you test will generate a “false positive” — the test will say he has Super-AIDS even though he doesn’t. That’s what “99 percent accurate” means: one percent wrong.
What’s one percent of one million?
1,000,000/100 = 10,000
One in a million people has Super-AIDS. If you test a million random people, you’ll probably only find one case of real Super-AIDS. But your test won’t identify one person as having Super-AIDS. It will identify 10,000 people as having it.
Your 99 percent accurate test will perform with 99.99 percent inaccuracy.
That’s the paradox of the false positive. When you try to find something really rare, your test’s accuracy has to match the rarity of the thing you’re looking for. If you’re trying to point at a single pixel on your screen, a sharp pencil is a good pointer: the pencil-tip is a lot smaller (more accurate) than the pixels. But a pencil-tip is no good at pointing at a single atom in your screen. For that, you need a pointer — a test — that’s one atom wide or less at the tip.
This is the paradox of the false positive, and here’s how it applies to terrorism:
Terrorists are really rare. In a city of twenty million like New York, there might be one or two terrorists. Maybe ten of them at the outside. 10/20,000,000 = 0.00005 percent. One twenty-thousandth of a percent.
That’s pretty rare all right. Now, say you’ve got some software that can sift through all the bank-records, or toll-pass records, or public transit records, or phone-call records in the city and catch terrorists 99 percent of the time.
In a pool of twenty million people, a 99 percent accurate test will identify two hundred thousand people as being terrorists. But only ten of them are terrorists. To catch ten bad guys, you have to haul in and investigate two hundred thousand innocent people.
Guess what? Terrorism tests aren’t anywhere close to 99 percent accurate. More like 60 percent accurate. Even 40 percent accurate, sometimes.
What this all meant was that the Department of Homeland Security had set itself up to fail badly. They were trying to spot incredibly rare events — a person is a terrorist — with inaccurate systems.
Is it any wonder we were able to make such a mess?
I stepped out the front door whistling on a Tuesday morning one week into the Operation False Positive. I was rockin’ out to some new music I’d downloaded from the Xnet the night before — lots of people sent M1k3y little digital gifts to say thank you for giving them hope.
I turned onto 23d Street and carefully took the narrow stone steps cut into the side of the hill. As I descended, I passed Mr Wiener Dog. I don’t know Mr Wiener Dog’s real name, but I see him nearly every day, walking his three panting wiener dogs up the staircase to the little parkette. Squeezing past them all on the stairs is pretty much impossible and I always end up tangled in a leash, knocked into someone’s front garden, or perched on the bumper of one of the cars parked next to the curb.
Mr Wiener Dog is clearly Someone Important, because he has a fancy watch and always wears a nice suit. I had mentally assumed that he worked down in the financial district.
Today as I brushed up against him, I triggered my arphid cloner, which was already loaded in the pocket of my leather jacket. The cloner sucked down the numbers off his credit-cards and his car-keys, his passport and the hundred-dollar bills in his wallet.
Even as it was doing that, it was flashing some of them with new numbers, taken from other people I’d brushed against. It was like switching the license-plates on a bunch of cars, but invisible and instantaneous. I smiled apologetically at Mr Wiener Dog and continued down the stairs. I stopped at three of the cars long enough to swap their FasTrak tags with numbers taken off of all the cars I’d gone past the day before.
You might think I was being a little aggro here, but I was cautious and conservative compared to a lot of the Xnetters. A couple girls in the Chemical Engineering program at UC Berkeley had figured out how to make a harmless substance out of kitchen products that would trip an explosive sniffer. They’d had a merry time sprinkling it on their profs’ briefcases and jackets, then hiding out and watching the same profs try to get into the auditoriums and libraries on campus, only to get flying-tackled by the new security squads that had sprung up everywhere.
Other people wanted to figure out how to dust envelopes with substances that would test positive for anthrax, but everyone else thought they were out of their minds. Luckily, it didn’t seem like they’d be able to figure it out.
I passed by San Francisco General Hospital and nodded with satisfaction as I saw the huge lines at the front doors. They had a police checkpoint too, of course, and there were enough Xnetters working as interns and cafeteria workers and whatnot there that everyone’s badges had been snarled up and swapped around. I’d read the security checks had tacked an hour onto everyone’s work day, and the unions were threatening to walk out unless the hospital did something about it.