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...