The ZuckerBorg collects so much data on its users that even visiting the site tags your ineffable soul for eternal tracking. But now a Harvard student's browser extension can now exploit the default location sharing setting to literally plot Facebook Messenger app users' movements on a map.

Aran Khanna, a CompSci student at Harvard, noted the location data leakage and wrote the Chrome extension Marauders Map to plot where his friends have been contacting him from.

Khanna says: "The Chrome extension was written to accompany my Medium post about the creepy potential of the location data we often inadvertently reveal about ourselves on Facebook Messenger, due to its defaults of always sharing your location when sending messages."

The blog post on Medium explains how Khanna mined a couple of weeks' worth of chat data and used it to build a picture of people's movements. "[L]ooking at the location clusters, you can even figure out [the sender's] weekly schedule. With this, you can predict exactly which building [they] would be in at a given time."

Khanna wrote that he found that he could even do this for people who he was not Facebook friends with. "I am currently in a large active chat to organise poker games with some fellow students, many of whom I am not Facebook friends with. However, I can still track their locations extremely accurately from the messages they send the group."

Although explaining his extension isn't working at the moment due to its sudden popularity, Khanna suggests a workaround. He notes that "due to the overwhelming response to this extension and my blog post, Mapbox (the service used to draw the maps) has revoked my API key, rendering this extension non-functional".

"You can still get this working by going on the Github, downloading the code and entering your own API key (which you can get for free from Mapbox)," says Khanna.

It is understood that Facebook are working on a fix for the location-leaking issue.

Khanna's shameless student bragging admirable commitment to honesty sees him disclose that he will be starting an internship at Facebook "on an unrelated team" in June 2015.

A Facebook mouthpiece told El Reg: “People share their location to better connect with their friends on Messenger. We've been listening to people's feedback and for the last few months have been working hard to improve this experience. We will be rolling out improvements very soon. In the meantime, people can still choose to turn off location sharing at any time by tapping the blue arrow in the message composer.”

Mischief managed. ®