What's changed: The Transportation Security Administration, created in November 2001, now oversees security screening in the nation's airports. Thousands of air marshals fly undercover on commercial flights.
What hasn't: While carry-on bags are screened for explosives, passengers are checked only for the metal kind. Cargo loaded onto passenger planes is rarely inspected as thoroughly as checked baggage.
What's changed: At facilities such as power reactors, the government has increased patrols, installed additional physical barriers, beefed up security forces in the area and expanded employee-background checks.
What hasn't: The security perimeters at nuclear sites remain vulnerable to attacks involving explosives. Though 52 airports are within five miles of nuclear plants, the airspace above such facilities is open.
What's changed: An integrated watch list makes the names of suspected terrorists available to border and law-enforcement authorities. A new biometric-screening system will make it easier to spot false identities.
What hasn't: Border-security agents lack technology and training to detect phony travel documents. Databases tracking entries and exits are not fully automated.
What's changed: The government erected air-sniffing sensors in dozens of cities to detect a chemical attack. The feds have committed $5.6 billion over the next decade to encourage drug companies to develop antidotes to bioterrorism attacks.
What hasn't: The country's hospital system remains unprepared for a sudden surge of patients in the event of a mass-casualty attack involving biological weapons.
What's changed: Rules adopted on July 1 require that ports have a specific security plan, which may include crew ID checks, X-ray machines and expanded baggage screening. The coast guard boards and searches all foreign vessels that enter u.s. waters.
What hasn't: Of the millions of shipping containers that enter the u.s. every year through 300 sea-and river ports, only a fraction are searched.
What's changed: The government has spent more than $100 million on improving security on trains, including heightened surveillance of high-risk trains, tracks and rail yards. Amtrak passenger names are checked against government watch lists.
What hasn't: Amtrak doesn't screen passenger baggage for weapons. about 25% of Amtrak riders never show identification before they board the train. --By Nadia Mustafa