The day after the University of Missouri’s president resigned following a series demonstrations over racism on campus, violent threats appeared on the anonymous messaging app Yik Yak. “I’m going to stand my ground tomorrow and shoot every black person I see,” one of the more alarming posts read.

That same day, another Yik Yak user threatened violence against black students at Northwest Missouri State University. A few days later, someone claiming to be a Missouri student threatened to kill black students at Howard University. Then, another Yik Yak user threatened to kill black students at Michigan Technological University. And last week, an anonymous user posted messages on Twitter, threatening to “shoot every black woman and male I see at Kean University.”

In the past two weeks, such threats have been made against more than a dozen colleges and universities. While many of the threats have targeted black students amid a growing campus protest movement, others seem to have been designed to capitalize on fear generated by the recent terrorist attacks in Paris. Some of the threats have been made against students at institutions that have attracted widespread attention for protests over racial issues, while others have been against institutions that have not had such protests.

Death threats targeting college campuses are not unusual, William Taylor, president of the International Association of Campus Law Enforcement Administrators and chief of police at San Jacinto College, said, but rarely do so many materialize within such a short time frame.

In the past week alone, there were shooting threats and bomb threats at Cape Cod Community College and Alvernia, Fitchburg State, Hampton, Harvard, Kean, Princeton and Saginaw Valley State Universities. No shootings took place, nor were any bombs found, but some institutions closed buildings or shut campuses out of precaution.

“There is greater number of these than I’ve seen before,” Taylor said. “There is an upswing with these types of threats being made this semester, especially with the tragedy in Oregon. It’s almost as if this whole semester has been building and building.”

In October, Oregon’s Umpqua Community College became the site of the third-most-deadly campus shooting in U.S. history when a gunman shot and killed nine people and injured seven more.

Hunter Park, the white college student who was arrested for making the threats against Missouri, had shown a “deep interest” in the Oregon massacre, according to court documents. The threat itself even used similar language: “Some of you are alright [sic]. Don’t go to campus tomorrow.” When Park was arrested, according to the court documents, an officer asked him what he meant. Park allegedly smiled and said, “I was quoting something.”

Ahead of the Oregon shooting, the alleged killer posted a brief warning on an online forum. “Some of you guys are alright,” he wrote. “Don’t go to school tomorrow if you are in the Northwest.”

The vagueness of the language used in both the Oregon and Missouri threats, Taylor said, illustrates just how difficult it is for college officials and law enforcement to determine which threats are legitimate and which are hoaxes. According to court documents, Hunter later told police he had just wanted to frighten Missouri students.

“Let’s face it, as a threat, ‘Don’t go to school tomorrow,’ is really a pretty general thing to say,” Taylor said. “Yet, look what happened at Oregon, where we saw the same general threat. And that threat turned out to be very real and very tragic. Any threat has to be taken seriously on its face, and so most institutions are erring on the side of caution.”

On Friday -- one week after a threat was posted online targeting students at the historically black university -- Howard University continued to be on alert, with increased security both on campus and at nearby subway stations.

“Terrorist acts, including anonymous threats of violence, are the antithesis of the university’s mission and that of a free and democratic society,” Wayne A. I. Frederick, Howard’s president, said in a statement. “As a university community and a nation that respects and embraces our differences, we cannot and will not cower to fear, hatred and discrimination. While the investigation of the online threat toward the university continues, including efforts to bring those responsible to justice, it underscores the need to remain vigilant.”

The threat was made by a person who claimed to be a Missouri student who came home to Maryland because he or she "couldn't put up" with the recent protests on campus. The author of the post said if any black students were on Howard's Washington campus or using the nearby subway stations, they would be killed. "Sometimes the best thing to do is to put stupid out of its misery," the person wrote. "After all, it's not murder if they're black."

On Tuesday, Alvernia University, in Pennsylvania, evacuated its campus for hours over a “safety threat.” Earlier that week, Harvard evacuated four buildings after a bomb threat. A bomb squad scoured the four buildings, but did not find anything. Most drastically, Washington College in Maryland announced on Wednesday that it will remain closed through at least Thanksgiving because of a police search for a missing student who was believed to be armed. The student’s parents told the college that he had retrieved a rifle case from his family’s home earlier in the week and disappeared.

On Saturday, authorities found the body of the student, Jacob Marberger, who died of a self-inflicted gunshot wound.

The student had recently been the victim of a prank, the college said, and allegedly brandished a handgun out of anger, though officials stressed they do not believe he directly threatened anyone. The incident led to his fraternity expelling him from the chapter, and he resigned from his role in the college's student government. After his disappearance, the campus was on lockdown for much of last week, before officials decided to close the college through Thanksgiving break.

"We would like to stress that there has been no direct threat to the campus or any members of its community or the region," the college said in a statement. "But in the interest of caution and for the sake of the emotional well-being of our students, parents, faculty and staff, this decision is the correct course of action."