Nearly 50 college campuses around the country have been hit in recent weeks by hoax calls warning of armed attackers and other violence, prompting lockdowns, canceled classes and hours of fear while testing the ability of dispatch centers to detect and contain false threats.

The bogus reports, sometimes delivered in mass batches and live-streamed by the callers’ associates, led students at some schools to hide under desks and forced law enforcement to divert time and resources from other duties. The FBI said it is investigating the incidents, but as of Thursday no arrests have been announced.

Several historically Black colleges and universities locked down or canceled classes after receiving threats this week, officials said, at a time when campuses were on edge following the fatal shooting of conservative activist Charlie Kirk at a Utah college and other recent attacks. Law enforcement officials and experts say the spate of hoaxes underscores a growing and evolving problem known as swatting, in which callers try to prompt an armed police response to a location by reporting a violent incident that is not happening.

Dispatch centers are frequently the last line of defense against swatting, but the calls can be difficult to spot immediately. Swatters commonly use voice-over-internet-protocol services and virtual private networks to mask their locations, and often call nonemergency police numbers to bypass 911 geolocation systems. That pattern has helped some dispatchers and police spot fraudulent calls quickly, but not always in time to prevent a full-scale response.

“You can’t just blow it off because there has been a bunch of hoaxes,” said Wendy Via, co-founder and CEO of the Global Project Against Hate and Extremism. “We have so many mass shootings in this country and so many young people die.”

The FBI said swatting is increasing. Since the agency set up a center in 2023 to collect information on such incidents, hundreds of law enforcement agencies have voluntarily submitted thousands of reports, the bureau said. The Department of Education has issued guidance for school officials on how to evaluate potentially fraudulent calls, suggesting follow-up questions about a caller’s phone number or location and noting other clues such as mispronounced campus names.

Experts tracking online extremist communities and threat actors have linked some recent calls to groups associated with an online network known as The Com. A group called Purgatory, tied to that network, has been connected to some of the swats, according to reporting by nonprofit researchers who reviewed livestreamed calls and shared recordings with news organizations. In more than two hours of livestreams reviewed by the researchers, the callers’ friends can be heard laughing and mocking the purported victims as the events unfold.

Keven Hendricks, a cybercrime instructor who trains law enforcement on swatting investigations and has been a target himself, said many of the calls appear motivated by amusement rather than political aims. “They were doing it for the LOLs,” Hendricks said.

Law enforcement officials described a recent incident at Kansas State University as illustrative. The initial red flag, said Major Daryl Ascher of the Riley County Police Department, was that the report did not come through 911. Emergency calls are geolocated and routed to the nearest dispatch center, whereas callers seeking to conceal their location often call nonemergency numbers. The caller also misnamed the school, referring to it as Kansas City State University, and described gunfire that sounded like pre-recorded effects, officials said.

Despite skepticism by dispatchers, officers were sent to the campus library to investigate. Ascher said dispatchers kept responding officers informed about inconsistencies in the call and that the response was scaled once the hoax became likely. He declined to provide the department’s recording of the call to news organizations.

Technology firms that monitor suspicious calls say automated defenses can blunt the impact of mass hoaxes. Don Beeler, chief executive of TDR Technology Solutions, which offers systems to screen for likely swatting calls, said suspicious calls can be routed to an automated recording instructing the caller to hang up and dial 911. He added that most swats would be prevented if systems stopped calls using VoIP services routed through VPNs.

The pattern of swatting stretches back decades and has roots in fake bomb threats and disputes in online gaming communities. Over time, it has evolved into organized campaigns by nihilistic online groups that trade tips for avoiding detection. When successful, the tactic can trigger a heavily armed law enforcement response to an address where no crime is taking place.

Officials say the calls are also taking an emotional toll on students and could erode trust in real alerts. “I hope we’re not desensitized enough to this to the point where we don’t take these alerts seriously anymore,” said Miceala Morano, a 21-year-old senior journalism major who took cover after a recent threat at the University of Arkansas.

Police agencies face a difficult balance: treating every threat seriously to protect lives while conserving limited resources and avoiding unnecessary escalation. The recent flurry of hoaxes came as law enforcement also responded to other violent incidents, including a shooting at a suburban Denver high school and an attack at a Minneapolis-area Catholic church that killed two schoolchildren and injured more than 20 people, events that have left campuses and communities particularly sensitive to any reports of gun violence.

The FBI declined to comment on specific reporting linking groups to individual calls but has urged anyone with information about swatting activity to contact the bureau. Nonprofit researchers said they have provided livestream recordings and other evidence to investigators. As agencies continue to investigate and technology firms refine screening tools, law enforcement officials said vigilance at dispatch centers and public awareness among students and staff remain critical to reducing the harm caused by hoax threats.

“The calls are very taxing on law enforcement,” Ascher said. “It often takes a lot of resources, and they can shake your faith.”