As more and more people are using cell phone apps to display boarding passes, this problem may eventually become non-existent. If, however, you still use printed boarding passes, you should probably shred, burn, or otherwise destroy them. Do not leave them laying around your airplane seat of casually toss them in the trash can at your destination gate.
According to the article linked below, there is a massive amount of personal information available on your boarding passes.
““Besides his name, frequent flyer number and other [personally identifiable information], I was able to get his record locator (a.k.a. “record key” for the Lufthansa flight he was taking that day,” Cory said. “I then proceeded to Lufthansa’s website and using his last name (which was encoded in the barcode) and the record locator was able to get access to his entire account. Not only could I see this one flight, but I could see ANY future flights that were booked to his frequent flyer number from the Star Alliance.”
The access granted by Lufthansa’s site also included his friend’s phone number, and the name of the person who booked the flight. More worrisome, Cory now had the ability to view all future flights tied to that frequent flyer account, change seats for the ticketed passengers, and even cancel any future flights.
The information contained in the boarding pass could make it easier for an attacker to reset the PIN number used to secure his friend’s Star Alliance frequent flyer account. For example, that information gets you past the early process of resetting a Star Alliance account PIN at United Airline’s “forgot PIN” Web site.”
Be careful out there.