University police said they investigated and determined the reports Tuesday night were false. But the rumors had already spread far and wide.
Another post contained a veiled threat.
Yik Yak is a social media app that allows users to share anonymous messages, or Yaks, with others in a 5-mile radius. However, the man police say they arrested early Wednesday for posting threats on Yik Yak and other social media -- Hunter M. Park, 19 -- was "contacted" in Rolla, more than 90 miles south of Columbia.
Park, who is from Lake St. Louis and is not a Mizzou student, was transferred to the campus police department, charged with making a terrorist threat and transferred to Boone County Jail where he was held on a $4,500 bond, police said.
It was unclear how police homed in on the suspect. One of the app's developers, Brooks Buffington, told CNNMoney earlier this year
that while federal law prohibited the sharing of personal information, "in cases of imminent threat or harm or something like that, we work with law enforcement to do what we can."
Even before the arrest was announced, campus police had said there was no imminent danger.
"Students need to be aware of what is going on, but right now there is no active threat on campus," police spokesman Maj. Brian Weimer said.
"The campus is not on lockdown. There is heightened awareness due to the national attention we are getting, but again the reports you are seeing on social media are largely inaccurate."
Police: No proof the KKK is on campus
Weimer said officers went to where the KKK was reported to be -- and found nothing.
"We have found no evidence of anything related to the KKK on campus," he said.
Student Body President Payton Head had already posted about it on Facebook.
"Students please take precaution. Stay away from the windows in residence halls. The KKK has been confirmed to be sighted on campus," Head wrote in a post that has since been deleted. "I'm working with the MUPD, the state trooper and the National Guard."
The police spokesman said the National Guard was not on campus, "nor have they been called to assist."
Head quickly apologized for spreading the rumor.
"I'm sorry about the misinformation that I have shared through social media," he posted on Facebook
"I received and shared information from multiple incorrect sources, which I deeply regret. The last thing needed is to incite more fear in the hearts of our community."
University officials toppled
African-American students at Missouri have long complained of an inadequate response by university leaders in dealing with racism on the overwhelmingly white Columbia campus.
Protesters clamored for change and for University System President Tim Wolfe to step down.
Former Mizzou wide receiver L'Damian Washington said he believes Wolfe took "a lackadaisical approach to get things fixed. ... I think (he) just turned a blind eye to it."
The protests got two major jolts when student leader Jonathan Butler launched a hunger strike
and the Missouri Tigers football team said it would not play until Wolfe stepped down.
The pressure worked. Wolfe resigned Monday
, followed hours later by Chancellor R. Bowen Loftin.
"Our campus has experienced significant turbulence, and many within our community have suffered threats against their lives and humanity. These threats are reprehensible," the school's leadership said Wednesday.
"The process of making our campus as inclusive as it must be will not be easy. We have difficult conversations ahead, and we must all dedicate ourselves to learning together," it read.
Marshall Allen, a member of the protest group Concerned Student 1950, said the change is just starting.
"This is just a beginning in dismantling systems of oppression in higher education, specifically the UM system," Allen said.
Media professor apologizes
During the height of the protests this week, professor and demonstrator Melissa Click was filmed grabbing a journalist's video camera, telling him he had no right to be there. She then asked for "muscle" to have him removed from the scene.
Click, to many people's surprise, was a professor of mass media.
After video of her outburst spread across social media, Click publicly apologized
She resigned her courtesy appointment with the journalism school, said the school's dean, David Kurpius. She also resigned her affiliation with the Chancellor's Student Publications Committee.
"I have enjoyed working with the faculty, staff, and students in both groups and deeply respect their missions," wrote Click, saying that she was resigning to "allow them to continue their important work without further distraction."
That doesn't mean Click is out of a job. She is still an assistant professor at the communication school, but the courtesy appointment gave her the ability to work with journalism doctoral students in topics that fall into her area of research, Kurpius said.
On Wednesday, another employee seen on the video was relieved of her duties.
Janna Basler, the director of Greek life and leadership, has been placed on administrative leave and relieved of her duties as director, pending an investigation of her actions, according to a statement from the head of student life.
In the video, Basler can be seen and heard telling a journalist, repeatedly, to "back off."
When he asks whether she is with the office of Greek life, Basler responds: "No, my name is Concerned Student of 1950."
How we got here
Protesters say racism at Mizzou -- sometimes blatant, sometimes subtle -- has simmered on campus for decades.
In 2010, white students scattered cotton balls
outside the Black Culture Center.
In September, Head -- the student body president -- vented on Facebook about bigotry and anti-homosexual and anti-transgender attitudes after people riding in the back of a pickup truck screamed racial slurs at him.
In October, someone used feces to draw a swastika
on the wall of a residence hall.
Even on Tuesday night, some reported incidents of threat or intimidation on campus.
"Im shaking and crying these white guys are in a monster blue pick up truck no license plate circling our car we almost couldnt get out," one student tweeted
Washington, the former football player, said it may be hard for a white person to understand.
"Only a minority knows what it feels like to be a minority on campus," he said.
The University of Missouri's Columbia campus has a population of 35,000 students. The undergraduate student body is about 79% white, and 8% African-American. The school's faculty is also more than 70% white, with black representation of just over 3%, according to the university.