On Nov. 24, when the decision not to indict Darren Wilson in the killing of Michael Brown was announced, some students protested peacefully. Others posted derogatory comments on the anonymous app Yik Yak.

Yik Yak is one of several apps that allows users to make anonymous posts. People can anonymously vote on and reply to posts, but only those made in their geographic area.

The Bowling Green feed got more negative throughout the night, said Kaylyn Collier, who manages external affairs for Black Student Union.

At first, people used the app to ask what was going on.

Then posts, or yaks, like “Everybody should go to sleep,” and “No one can hear you,” started appearing, Collier said.

The yaks got negative, and untrue. “Now they’re in the Union breaking TVs and rioting,” was an example

Collier gave.

The negativity wasn’t unexpected.

“I was not surprised at all,” Collier said. “My organization has already been attacked on social media before.”

The difference this time was the complete anonymity of the attackers.

“It gives people courage and this invincibility,”

Collier said.

According to the app’s “Rules & Info” page, users can report yaks that are “useless or offensive.”

In some cases, police response to yaks has been necessary. The LA Times reported that San Clemente High School went into a four-hour lockdown this past March so that a bomb squad could search the campus after a bomb threat was posted on Yik Yak.

Another lockdown happened Nov. 20 in response to a shooting threat at Torrey Pines High School, also

in California.

Since geographic location is an essential part of the app, the developers blocked the app from working at middle and high schools.

The app can be used for good, though. Tech Cocktail reported that at Vanderbilt University, a student used the app to promote a drive where people could get their mouths swabbed to find a person who could give a blood transfusion to a lymphoma cancer patient.

The app’s creators are hopeful that that’s the type of result that will happen more often.

“Anonymity can be a really beautiful thing, and one of the reasons we made it anonymous is it gives people a blank slate to work from, so you’re not judged on your race or sexuality or gender,” said Yik Yak co-founder Brooks Buffington during an interview with CNN. “On Yik Yak you are purely judged on content you create.”