"This is a huge concern," said Mary F. Schiavo, aviation attorney and former Inspector General for the U.S. Department of Transportation. "The attackers don't have to die with the plane, which leaves for the terrorists a much bigger group of co-conspirators."
The Transportation Security Administration says that as of August of this year, all cargo on passenger aircraft originating in the U.S. is screened. Methods include sniffer dogs, X-ray machines and hand checks.
But just two-thirds of cargo on inbound international passenger air carriers is screened. The TSA wants to boost that to 100 percent by 2013. Cargo planes are subject to unannounced inspections and other security protocols -- the TSA doesn't say what percentage of cargo is checked.
Shipping is also a potential target. Most containers coming into ports aren't inspected, said Thomas Mockaitis, a DePaul University history professor who teaches government-funded seminars on counter-terrorism. "If we're doing 10 percent or more, I'd be surprised," Mockaitis said.
"Terrorists are methodical and they're patient," said Philip Farina, CEO of Farina and Associates, whose services include security and risk management.
"They're going to work the weak links. . . . If it's stronger on the passenger side and weaker on the cargo side, they're going to take a look at that weak side and exploit that."
In response to the Yemen plot, the Department of Homeland Security ordered a halt to all air cargo coming from Yemen and Somalia. DHS also directed industry carriers to start adding additional security measures for international flights inbound to the United States. Toner and ink cartridges over 16 ounces are banned in both carry-on and checked bags on passenger planes, and on some inbound air cargo shipments.
TSA Administrator John Pistole said the agency is working with the industry to develop new technologies for air cargo screening.
But screening every piece of cargo coming in and out of the country on boats and planes would drive shipping companies out of business, analysts warn.
As with passengers, screening cargo requires a balancing act between what could increase safety and what's practical. Cavity searches of airline passengers might deter terrorists -- but would also guarantee that many people would never fly again.
Similarly, there has to be a way to allow cargo to be shipped that would balance fears of terrorism against destroying trade, Mockaitis said.
"If you want to live in an open society, there's a certain level of risk you're going to have to accept," Mockaitis said.
For heightened security, governments need to watch not only passengers but people who have access to storage facilities and aircraft, to prevent the possibility of someone smuggling something onto a plane. He thinks O'Hare does "a very good job of making sure everyone's badged and certified."
U.S. officials need to continue to work with other countries and their police and customs departments to establish strong relationships and share intelligence, said Farina. Good intelligence is what led to the detection of the Yemen plot.
The Yemen crisis also highlighted the need to have heightened standards for anything that comes from certain countries in the Middle East, said DePaul University Transportation Professor Joseph Schwieterman. "It's going to take far more vigilance than we've had in the past," he said.
Nothing is fool-proof -- the world of trade is very complex and interconnected, and terrorists are extremely creative, said Mockaitis.
"You can get the best hockey goalie in the world, but you'll never find a goalie that's never been scored on," he said. "You have to make it very hard."
Mockaitis said travelers should take some encouragement from the fact that recent plots against American air travel have been stopped. He said when people say they'll stop flying because they're afraid of terrorists, they should remember it's statistically much more dangerous to drive a car.
"You don't want to become hostage to your own fears," he said. | 
