While law enforcement officers beef up security around threatened sites in New York City, New Jersey and Washington, D.C., after seized computer files showed Al Qaeda (search) targeting specific sites in those cities, a quick look around shows major vulnerabilities in each of those places and elsewhere.

Homeland Security officials named five buildings last week that were mentioned in the seized materials. They add that evidence suggests Al Qaeda also has continued interest in attacking the Capitol (search) building in Washington, D.C., and in killing members of Congress.

Truck or vehicular bombs like the one used in the Oklahoma City bombing (search) by homegrown terrorist Tim McVeigh can have a devastating impact. And though law enforcement has fortified Washington, D.C., adding jersey walls in many places and loading up on the police presence downtown — a quick tour downtown shows that a truck bomb could easily roll under or nearby the Department of Labor (search), the new addition to the D.C. Court of Appeals and the Kennedy Center.

Those routes are hardly secretive. Rush-hour traffic daily travels under those buildings as well as others, like the Department of Energy (search).

Click in the video box near the top of the story to watch a report by FOX News' Brian Wilson.