PORTLAND, Ore. - Kiosks are meant to speed up the check-in process at the airport, but security experts say they could be open doors for terrorists to hide their identities on U.S. jets.

Our investigation began when a frequent flyer on the nation's third-largest air carrier, United Airlines, wrote to KATU News explaining how easy it would be for someone to get their hands on someone else's boarding passes using the airline's kiosks.

We wanted to see if the claim was real, so we headed to Portland International Airport with a hidden camera to find out.

Using a credit card belonging to KATU Photojournalist Brian Smith, we found what we were looking for in no time.

Just by slipping his credit card into the kiosk and punching in his name, we had access to 21 different Brian Smiths flying United Airlines. We could have chosen any flight we wanted to on the list and printed the boarding passes using someone else's identity.

With the help of ABC7's On Your Side Investigator Michael Finney, we found the same thing at San Francisco International where Portland-bound passenger John Baker discovered numerous options to fly as another John Baker, or even Janet or Jeanne Baker.

Vincent Yee, a frequent flyer on United, said it happens to him all the time and he has to be careful not to print the wrong boarding pass.

In San Diego, a United passenger told our team he had accidentally printed the wrong boarding pass before and nearly made it through TSA screening.

Everywhere we turned, people checking in at United kiosks were able to print boarding passes of others with similar names, departing that same airport.

Michael Irwin, Portland's TSA Federal Security Director, said it is an airline issue, not an issue for his security screeners.

"What we do when folks come up, we look at their ID, their government-issued ID, along with the boarding passes to ensure that you are the person you say you are," he said. "Then we make sure everyone goes through the same screening process."

Unfortunately, security is not iron clad. For example, a team of covert investigators from the Government Accountability Office were able to smuggle an explosive in carry-on luggage at a number of U.S. airports.  In fact, 90 percent of the time they were able to get through security with the explosive.

As alarming as that is, we wanted to know if someone could possibly get through TSA screening with an explosive using another person's identity from a United Airlines kiosk.

That would take a fake ID, or possibly a real one obtained using a stolen identity, something ID theft expert Ronald Williams said is simple.

Williams spent 22 years with the Secret Service overseeing credit card and financial fraud units, and the elite counter assault team to combat terrorism.

He said the very people TSA is trying to keep off of airplanes are the same ones leading the way in counterfeit credit cards that could conveniently be used at kiosks and bogus IDs that could be passed at TSA checkpoints.

"You have street gangs in L.A. doing it," Williams said.  "More disturbing than any of it is that the terrorist groups are into it."

And the last line of defense are the TSA security screeners, many of whom failed miserably in the GAO's investigation.

"Granted, TSA is highly trained to prevent this, but the potential is still there," said Aviation Security Consultant Glenn Winn.  "It's human error."

Winn is the President of Aviation Security Consulting and was a former secret agent assigned to the Presidential detail.  He also spent 15 years as the head of security for United Airlines.

"I would suggest that the airlines address this as soon as possible with their computer experts and figure out what the problem is," he said.  "It's got to be fixed and convenience, as I say, is a second point in all of this.  Security and safety is number one."

United Airlines issued a statement in response to our joint investigation:

"Safety is our number one priority and that's why there are several layers of security after check-in and throughout the airport.  Our kiosks are very popular with our customers who use them to quicken their check-in, conveniently request an upgrade and easily standby for earlier flights."

The GAO made several recommendations to tighten security, saying TSA needs more people, more training, new policies and new technology.  However, as the TSA chief in Portland told us, the airlines are going to have to do their part to help make sure the people who are supposed to be getting on airplanes are the same people who are getting boarding passes.

Note: Our team also tried to get boarding passes at kiosks for Delta, Jet Blue and Southwest Airlines, but security measures were already in place to prevent anyone but the person who made the reservation from accessing the names of the other passengers or printing their tickets.