You're so excited about your upcoming vacation that you post a pic of your boarding pass on social media. If you've done this, trust us, you're not alone. Even more people toss their "used" boarding passes on the floor of the airplane. Both of these are bad ideas.

Why? Because boarding passes contain more private data than you probably realize. In fact, we should probably think of treating them less like valet tickets for a parked car and more like social security numbers.

Related: Who Needs Travel Insurance? You Might

Tech reporter Brian Krebs explained in a blog post that "two-dimensional barcodes and QR codes can hold a great deal of information, and the codes printed on airline boarding passes may allow someone to discover more about you, your future travel plans, and your frequent flyer account."

Decoding your boarding pass is actually fairly easy, according to Krebs. Anyone can upload a photo (or screenshot, if it's on social media) of your boarding pass to a free online barcode reader and find your reservation, frequent flyer number, full name and arrival and departure airports. In theory a hacker could change your upcoming flights — or cancel them — with just a few clicks on the airline's website.

A determined hacker could even try to answer your security questions — which he could guess at after some light social media stalking — to get more of your personal information. Think your mother's maiden name or the name of your pet — much of this can probably be found on your social media feed by a stranger if you don't have the right privacy settings. (Another good reason to make sure you're sharing information only with friends and family.)

Boarding pass barcodes were introduced in 2005 by the International Air Transport Association in an effort to eliminate magnetic boarding passes, use cheaper paper stock and enable mobile technology.

While the content of the barcode might differ from airline to airline, it pays to be careful. The best thing to do is to hold on to your boarding pass and then shred it when you get back home, according to Krebs — just as you'd shred credit card offers, bank statements and other documents bearing important personal information.

If you don't want to worry about it every time you fly, skip the paper and have the boarding pass sent to your mobile phone instead.

Related: Travel Abroad Checklist: 8 Documents You Need

Muriel Vega is a writer with a passion for budget travel and staying safe while abroad. A Georgia State University graduate, she has over 6 years of editorial experience and has written for The Guardian, The Atlantic, The Billfold, among other outlets. In her free time, you can find her baking pies, playing with her two dogs and cat, or planning her next vacation. She spends way too much time on Twitter, one of her favorite social media channels. Her favorite safety tip: Make sure you have all the necessary shots before you go abroad.