Use Facebook Messenger? Marauders Map app can pinpoint your location to within 3 feet

Stalkers will likely rejoice as a new app can help them do more than creep on Facebook friends; it can pinpoint the precise location of non-friends if they use Messenger to post to the same group and the sender hasn't disabled location sharing.

App for stalkers
Kelly Hau (Creative Commons BY or BY-SA)

If you use the Facebook Messenger app, would you be comfortable knowing your location can be pinpointed to less than a meter?

Sure Facebook shares your location with your friends, but did you know that if you use Messenger to group chat with someone who is not a friend, then that person can now find out not just what town you were chatting from, but longitude and latitude coordinates of where you did your chatting? Those coordinates are reportedly accurate to less than three feet from where you sent the message, according to Aran Khanna, a computer science and mathematics student at Harvard, who created a creepy new Chrome extension called Marauders Map to help you stalk your friends with Facebook Messenger.

Before we dig into Marauders Map, you need to know there is no reason to freak out and panic as the pinpointing app only works if you left location services for Messenger enabled. Hopefully you turned off location sharing back when Facebook had to defend its reasons for Messenger permissions to access a phone’s camera and microphone. If you aren’t sure, then location is probably on as Facebook tends to snub privacy-by-design options; location sharing is on by default.

Khanna, who named Marauders Map after Harry Potter’s magical map capable of tracking people, said, “I decided to write this extension, because we are constantly being told how we are losing privacy with the increasing digitization of our lives, however the consequences never seem tangible. With this code you can see for yourself the potentially invasive usage of the information you share, and decide for yourself if this is something you should worry about.”

If you install Marauders Map, then it will bring up a map each time you open Messenger.

Facebook Messenger and Marauders Map Aran Khanna

His code “scrapes every Facebook message sent by your friends or you with a location attached and then plots those locations chronologically on a map.”

Facebook Messenger location data via Marauders Map Aran Khanna

In a post on Medium, Khanna wrote:

Go ahead and see how many messages in your chats have locations attached. I’m guessing it’s a lot of them. And if this isn't already starting to get a bit weird, the first thing I noticed when I started to write my code was that the latitude and longitude coordinates of the message locations have more than 5 decimal places of precision, making it possible to pinpoint the sender’s location to less than a meter.

Marauders Map Aran Khanna

Even if the app weren’t that precise, how close is too close when it comes to people knowing your location? Are your Facebook friends also in-real-life friends? Would you be cool with a non-friend knowing your location if it were within 15 to 30 feet? It still seems too creepy even at 30 feet, 10 times the distance Marauders Map can allegedly pinpoint location.

If you are OK with a fairly accurate accounting of your location being scraped, then consider that plotting your chat location data on a map over time means that someone can figure out your schedule and predict where you will be at a given time. That’s what Khanna did; he was able to obtain a “detailed location history” of someone he was not friends with on Facebook. In fact, since he participates in several group chats, he used Marauders Map to “infer a schedule for almost everyone” from those various chats.

He added, “Everyone I have shown this extension to has been anywhere from surprised to appalled that this much of their very personal data is online for their friends (and even complete strangers) to access.”

How to tell if you are sharing location with Facebook Messenger Aran Khanna

I’m not a fan of Facebook and that is why I am using his images, but I had someone who does use Messenger check it out; as if it were a new toy, he then immediately start creeping on his friends. Hypothetically, if you and your ex are in the same group and you both still post to it, then if your ex has location enabled you could map all of his or her locations. The same is true if you wanted to stalk someone . . . or if someone wanted to stalk you.

Yet on GitHub where Khanna shared his open source code, he wrote, “This is not meant to be used as a tool to creep on your friends, rather a demonstration of the scary amount of information you can gather on someone just by aggregating the data they provide through Messenger. Hence I made no attempts to facilitate the data generation process, and I ensured that all gathered data disappears on page reload.”

Facebook, where Khanna will begin an internship in June, said location with Messenger mobile app is included when you send a message, but “your location won’t appear anywhere outside of the message.” That’s no longer true thanks to Marauders Map, but Facebook said you can turn off the location-sharing “feature:”

You can turn this feature off for an individual conversation by tapping the location icon before you send a message, which turns the icon from blue (on) to gray (off). If you tap to turn location off, it will remain off for that conversation until you tap the arrow again.

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