It is now easier (and creepier) than ever to stalk your friends, thanks to a new Chrome extension appropriately dubbed Marauders Map. And just as with the Harry Potter version, using it means you're probably up to no good. Through data shared with Facebook Messenger, Marauders Map is able to pull your friends' locations based on where they were when they sent messages, and plot them on a map. The extension's creator, Aran Khanna wrote this post on Medium detailing what the extension does and why he made it. "By simply looking at the cluster of messages sent late at night, you can tell exactly where his dorm is," Khanna says about a friend from Stanford, "and in fact, approximately where his room is located in that dorm." But wait, it gets creepier. Khanna writes, "by gathering a couple weeks’ worth of chat data on the map and looking at the location clusters, you can even figure out his weekly schedule. With this, you can predict exactly which building he would be in at a given time." Your Facebook friends have no idea when you use the extension, which makes these check-ins silent and eerily sneaky. It's a certainly dream come true for stalkers, but Khanna didn't create the tool to be a creep. He explains, "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." Facebook Messenger shares your location by default, so you'll have to manually turn it off to prevent something like Marauders Map from accessing it — which we highly recommend doing, unless you're cool with every one of your Facebook friends having the tools to trace your every move. To do this on Android, go to the menu icon, Settings, Location Services, then de-select the box that enables location services for the app. Similarly, on iOS, go to Settings, Privacy, Location Services, and switch it to "Never" for Facebook Messenger.