You see them all over – littered on the ground, in seat-back pockets, and casually dropped in airport trash cans. I’m talking about boarding passes of course. Read on to find out why you are making a critical mistake if you casually discard them after your flight.

The One Critical Piece of Information That Every Boarding Pass Contains

Every boarding pass, regardless of airline, contains an essential piece of information that can compromise your identity if it falls into the wrong hands. Located on your boarding, sometimes conspicuously sometimes in small print, is your record locator, typically a six-character combination of letters and/or numbers that airlines use to store your reservation. In other words, this is the tracking code for your ticket. With that confirmation code comes the ability to do a number of potentially devious things including changing and cancelling remaining flights, gaining personal information like telephone numbers and e-mail addresses, and perhaps most perniciously gaining frequent flyer numbers, which can be used to steal your miles!

Here’s an example. Say you booked a ticket from Chicago to Dallas and back and casually leave your boarding pass in your seat-back pocket upon arrival in Dallas. Now assume someone picks it up with a bad intent. You’ve given them everything they need. By inputting the record locator and your name into the airline’s online homepage, your return trip will come up and (depending upon the airline) so will your contact details and frequent flyer info. Without even picking up the phone, your return reservation can be cancelled or modified online – it just takes a few clicks. Even more sinister, if that person wants to steal your return journey, the reservation can be changed – no password necessary.

Here’s how it would play out. Thief gets your boarding pass on the aircraft or in terminal, modifies your return, uses a smart phone or airport kiosk to check-in (no ID required), then board with your boarding pass (no ID required). That assumes the thief is resourceful enough to get on the secure side of the airport, but that’s not hard – a refundable ticket can quickly get one through security. Buy a ticket, check-in, go through security, then cancel the ticket. Voila!

But that’s not even the worst thing that can happen. Your boarding pass either has your corresponding frequent number printed directly on it or even if it is x-ed out, you can get it online with the record locator. This is true with Delta, with American, and with United – an equal-opportunity security breach. United and Delta are ostensibly more secure, with the former requiring a PIN code for any mileage redemption and the latter requiring a password, but those security requirements are laughably easy to bypass. With the confirmation number you have the full name, frequent flyer number, telephone number, e-mail address – it’s not hard to do a little googling to get the rest and airlines are not going to be asking for mother’s maiden name, only addresses and telephone numbers, perhaps a birth date. It’s all available online. With a couple of questions answered correctly (and many trusting agents won’t even bother to ask), you’re “in” and can take miles, upgrades, even reset passwords and access even more personal information on file with the airline.

What Info You Can Get with an American Airlines’ Boarding Pass

Just what can you get with an American Airlines boarding pass? With confirmation number in hand, you can pull up anyone’s reservation and you will immediately see their flight details, frequent flyer number, telephone number, and e-mail address:

What Info You Can Get with a Delta Air Lines’ Boarding Pass

With a Delta confirmation number, you can get Skymiles number, e-mail address, and telephone number. You can also change and cancel flights without logging in.

What Info You Can Get with a United Airlines’ Boarding Pass

United Airlines tries – even with a boarding pass the MileagePlus number is x-ed out and once you pull up the reservation online, the MileagePlus number is again x-ed out on the receipt and in the passenger information section.

But United always leaves a loophole. Just click on “e-mail itinerary” and the full MileagePlus number shows up.

If only that was it…you can also modify and cancel reservations easily with no login. Just click “cancel” and “cancel” once again and the reservation will be fully cancelled.

How to Prevent Theft: Keep Your Boarding Pass

The good news is there is a rather easy way to avoid this problem: keep your boarding pass close. Use a smart phone when possible to display your boarding pass but if you do have to print the boarding pass, keep in your pocket and double check the floor around your seat and seat back-pocket to ensure you have not left it behind.

While I don’t think there are hundreds of crooks lurking around airports for discarded boarding passes, I’ve heard horror stories and I don’t want you to have a horror story of your own, so do yourself a favor and keep your boarding pass close.