Three lessons from the Times Square bomb.

This may explain why busy areas like Times Square aren't attacked by terrorists more often. The crowds make them tempting targets: lots of people mean lots of potential victims and subsequent media attention. But those same crowds—especially the regulars, who are always looking out on the street—make an attack harder to conceal and, therefore, to pull off. (Research project for a sociologist: Have terrorist attacks in Western cities taken place more often, or less often, in areas with lots of street vendors?)

3. Security cameras may be OK. As has widely been reported, the Times Square car bomber may have been captured on surveillance cameras. Someone was videotaped, in any case, walking away from the van and furtively looking around. Someone who just happened to be taking pictures in the area caught what appeared to be this same man, moments later, running up Broadway. If this turns out to be the bomber, and if the pictures help the police identify and find him, the use—and popularity—of public security cameras will certainly get a boost.

A 2006 Harris poll showed two-thirds of Americans favored expanding the use of such cameras, though three-quarters expressed concerns about civil-liberties safeguards. At the time, more than 200 cities in 37 states had installed cameras in public places—not counting those with cameras to monitor traffic violations.

After the Sept. 11 attacks, the New York Police Department set up a massive array of cameras in Lower Manhattan—well over 4,000of them—modeled after London's "ring of steel" surveillance network. The city recently received a grant from the Department of Homeland Security to install a similar system in Midtown.

In 2008, the New York Civil Liberties Union filed a lawsuit against the NYPD, demanding more information about these cameras—how much the system costs, who can examine the footage, how long it's kept, whether it's destroyed. It's worth noting that the suit, which is still pending, calls only for information, not for imposing restrictions on the system or shutting it down. This morning, when I asked about the NYCLU's viewpoint on public surveillance cameras generally, a spokeswoman told me, "It's a complicated issue."

These cameras are probably permanent fixtures in American cities. And city dwellers (as well as tourists) may have come to accept that privacy cannot be presumed when they're out on public streets.

Correction, May 4, 2010: This story originally misspelled Lance Orton's forename. (Return  to the corrected sentence.)

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