Security expert Bruce Schneier must be screaming from wherever he is at the U.S. reaction to this morning's bombings in London. The immediate reaction was a tightening down of mass transit in the United States and an increase in the terror alert level. The New York Times reports:

Thousands of police officers in New York were dispatched to guard bridges, rail and bus stations - many of them staying on for hours after their shifts - where they were patrolling on foot and monitoring tunnels with video surveillance equipment.

Governor Pataki has signed an executive order authorizing state police officers from New Jersey and Connecticut to provide security on trains coming into New York. The increased police presence will remain in the city through the Friday rush, Commissioner Kelly said.

Counterterrorism officers are inspecting subway trains and "suspicious" luggage with bomb-sniffing dogs, Mayor Bloomberg said. Police helicopters are monitoring harbors, sea marshal patrols have been stepped up, and more officers are being posted aboard ferries and at the St. George and Whitehall Ferry terminals, he said.

Is this really the correct reaction? Bruce Schneier says no. In an interview with IT Conversations last year, Schneier talked about how the United States is really good at preventing against what terrorists have already done:

One of the things I'm always struck with is how good we are at defending against what the terrorists did last year. We're spending a lot of money shoring up our airlines and now we're talking about shoring up our trains, and money that we spend that simply causes the bad guys to change their tactics is money wasted. You have a red and a blue door, and the terrorists go through the red door, and you say, "We must secure the red door," so they go through the blue door next time. So what did you actually buy? And one of my fears is that you spend a lot of money securing the airlines and the terrorists move on to shopping malls or movie theaters or crowded restaurants. There are just so many targets that taking the target that terrorists happened to pick last year and securing it just sort of ignores the real problem.

This is exactly what we're doing in the United States: trying to protect against what the terrorists have already done. If they're smart, they will change their tactics for their next attack. Like the Borg, they constantly adapt. The only way they'll use the same method multiple times is if they are attacking several places simultaneously, as they did today.

Of course, in the same interview, Schneier says that we should do whatever makes people feel safe even if it won't actually make them safer. Sometimes, though, this is not feasible. A host on MSNBC asked former NYPD chief Bernard Kerrick if it would be feasible to institute airline-style security on the New York City subway system. Kerrick replied that it wouldn't be feasible, since there are 100,000 people in Grand Central Station during the morning rush hour, and attempting to institute metal detectors and wanding would create more than a bottleneck and defeat the purpose of having a subway system at all.

What is the answer then? As Schneier says, attempting to secure the targets is like treating a disease's symptoms and not its cause. It's a long-term fix, but ultimately, to reduce terrorism and make the populace safer, we must institute policies that address the reasons why people commit terrorist acts in the first place. There are far too many places where people congregate in large groups for us to be able to secure all of them.