On campuses across the country, millions of students have an app called Yik Yak on their phones.
It's like an anonymous version of Twitter. But because it's anonymous, it can get ugly and be a breeding ground for hate speech.
Black student leaders across the country have held sit-ins and protests asking college officials to block the app.
Yik Yak, an Atlanta-based social media app, has a presence on more than 2,000 college campuses. Users of the app post comments anonymously, and anyone in within a radius of a few miles can see, share and rate the comment.
Nikolai Yudin, a freshman at Atlanta's Emory University, describes it this way: "It's a forum for people to post anonymous thoughts and some of those thoughts are potentially offensive to others but at the same time, I mean, not that I've ever seen anything groundbreaking, like 'wow, what a great share,' but sometimes some things are funny."
Mostly, users post innocent jokes about bad breakups or awful dining hall food. But students have targeted minorities and made death threats.
At Western Washington University, there were calls to lynch the black student body president.
At the University of Missouri, students threatened to shoot all black students.
It's not just students of color: Posts also have threatened lesbian, gay, bisexual and transgender students.
At Kenyon College in Ohio, an anonymous commenter proposed a gang rape at the school's women's center.
And in October, a student at Emory's Oxford College campus was arrested after she posted a message on the app threatening to shoot everyone.
At least half a dozen universities have blocked the app on their Wi-Fi networks. Now, some students at Emory are calling for more: blocking Yik Yak completely, even for people who access it via a cellphone.
"For a while it was just kind of a lighthearted app," says Kaya Ruffin, a sophomore at Emory.
But then some users took it to the extreme.
It became "a medium for a lot of hate that's very race-targeted and very gender-targeted, so it's just kind of a downer," Ruffin says. "So I just avoid it."
Black students like Manzi Ngaiza say they feel targeted.
"It's not like this is some kid on a YouTube channel," Ngaiza says. "It's someone in your geographical area, so you know the fact that you're in class with someone who really feels that they need to share this sentiment of like 'Black kids at Emory need to go back to Africa.' It's not a good feeling obviously."
Some students want Yik Yak to set up a "geofence" around the zip codes of Emory University to block the app.
Jason Wong of Gartner Research is an expert who helps businesses develop mobile apps.
"They call it fencing because it implies a boundary of some sort that's based on location and whether you're in the boundary or outside that boundary, you get a different experience," he explains.
Geofencing often uses technology much more sophisticated than just GPS coordinates.
Advertisers use it inside stores — for instance, promoting bananas on customers' cellphones when they're in the produce aisle, and nudging them to buy deodorant when they're in the health and beauty aisle.
One way Yik Yak uses geofences is to block the app entirely at middle and high schools. That's because it's meant for users over the age of 17.
Still, Wong says, there are always workarounds.
"I think it's a much better policy to explore why people are using an application and maybe explain to people why they shouldn't be using it as opposed to just simply blocking it," he says.
Blocking Yik Yak from Emory is kind of like shooting the messenger. Senior Manik Soi says students can still post offensive comments elsewhere.
"There are other things like Emory Secrets where people post such hateful stuff as well. I don't see the college banning that, right?" Soi says.
Emory University says it doesn't have a position on Yik Yak, but administrators say they will speak with black student leaders and set up a task force on the possibility of a geofence.
Yik Yak declined to comment for this story.