Updating your location on social media can let your friends know where you are, but they may not be the only ones keeping up with you. According to a CNBC report, Facebook tracks users it deems threatening through a “Be On the Lookout” or BOLO list.

Facebook looks through its social network for any potentially threatening comments, as outlined by the report. Those can be nonspecific threats to a Facebook office or one actually targeting specific people.

Created in 2008, the BOLO list now contains hundreds of people and is updated about once a week, four former Facebook security employees told CNBC. When placed on the list, Facebook can track users’ locations using their smartphone’s location data collected by the app or their IP address collected by Facebook’s website.

Tracking threats is reasonable, but there are no clear outlines as to what a ‘credible’ threat is. For example, the report said a vague complaint like “Fuck you, Mark” could get you placed on the list. Users aren’t notified when they’re added.

There is good reason to be wary of Facebook’s judgment. Facebook is wildly inconsistent when it comes to implementing community standards on its site. Users are banned for saying “men are trash,” for example, while Mic reported InfoWars host Alex Jones was allowed to spread misinformation and incite harassment for years.

In addition, CNBC noted that other platforms may use similar methods to track threats, but they don’t have access to real-time locations and other key data like Facebook does.

Facebook has also been used by the FBI for tracking “Black Identity Extremists.” In December of 2017, Rakem Balogun was arrested by FBI agents investigating “domestic terrorism” throughthe monitoring of his Facebook posts, as reported by The Guardian.

A former employee called Facebook’s tactics “very Big Brother-esque,” as reported by CNBC. The creation of any lists designed to monitor users with vague guidelines is a little concerning.