Alison Dirr

USA TODAY NETWORK-Wisconsin

APPLETON - A wave of threats directed at schools across the nation Monday forced authorities to lock down buildings or evacuate students.

The threats, which appear to be driven by automated calls, have been directed at elementary, middle and high schools in states across at least four time zones.

Some districts reported that the calls included a bomb threat while others just described the calls as "threatening."

The calls were reported in California, Colorado, Delaware, Florida, Iowa, Maine, Maryland, Massachusetts, Minnesota, Montana, New Hampshire, Oregon, Pennsylvania, Utah, Vermont, Washington and Wisconsin.

Ken Trump, a national school security expert and president of a school security consulting firm, said Monday’s nationwide bomb hoaxes have the hallmarks of swatting.

Swatting, according to Trump, are “highly disruptive” hoax threats that are intended to trigger massive police response. Trump said they are often described as robotic, computer-generated voices that call in threats to schools or police departments.

A single swatting case can impact multiple states, jurisdictions and even travel across international borders, Trump said.

“They tend to come in waves,” he said. “We’ve seen them cross six states in an afternoon.”

Trump said swatting incidents have “skyrocketed” nationwide in the past two years.

“(Swatting) suspects are often more sophisticated,” he said. “They can use Voice Over IP (Internet Protocol) systems or other technologies that can be virtually impossible to track down.”

The Federal Bureau of Investigation responded to request for comment, writing, "We are aware of recent bomb threats at various schools in different states, and we remain in touch with our law enforcement partners to provide assistance if needed. As always, we encourage the public to remain vigilant and to promptly report suspicious activities which could represent a threat to public safety."

Lee Allinger, superintendent of schools in Appleton, Wisconsin, said he can't remember a string of threats so widespread that seem to be connected. Janet Berry Elementary School in Appleton received an automated threat about 11:45 a.m.

"It's the first one that I can recall that's been of this nature, where it's been an automated call or a robo kind of call and that it's been widespread — not just next door to us but across the state and the country," he said.

Tom McCarthy, a Wisconsin Department of Public Instruction spokesperson, said the department did not know how many schools statewide had received threats. He did not comment on the string of bomb hoaxes.

In the United Kingdom, at least 21 schools received bomb threats, as well, according to The Independent.

The USA TODAY NETWORK has yet to confirm that the threats are connected.

California

Clairemont and Lincoln high schools (San Diego): The schools were placed on lockdown after officials received threats. Police swept the schools and lifted the lockdown after nothing suspicious was found

Washington Middle School (Bakersfield): The school went into a lockdown Monday morning after receiving an anonymous bomb threat. Police officers and a police dog searched the school and surrounding area. School resumed after the area was determined to be safe. The call sounded like it was automated.

Colorado

Cherokee Trail Elementary (Parker): Students were evacuated Monday afternoon after “anonymous threats to schools around the state,” the Parker Police Department said in a tweet. Parents and caregivers were able to pick up their children, and some streets around the school were closed off.

Irish Elementary School (Fort Collins): Students were evacuated after a recorded phone call came in at 11:30 a.m. No credible threat was found. Students returned to class half an hour after they were evacuated.

Lakewood High School: The school received a threat by phone that officials believe was automated. Officials did not evacuate the school because the school district has received automated threats previously this school year.

Liberty Point Elementary School (Pueblo West): Officials evacuated the school shortly after 1 p.m. after a bomb threat was received.

Nevin J. Platt Middle School (Boulder): The middle school was swept by local law enforcement after someone left an automated threat.

The Colorado Springs School: The school was evacuated and students were sent to Broadmoor Elementary School after the school received a bomb threat.

Delaware

Bomb threats were reported at six Delaware schools.

East Millsboro Elementary School: Police learned at 11:09 a.m. that a man had called the school and said there was a bomb inside. Beacon Middle School in Lewes, Polytech High School in Woodside and Stanton Middle School in Wilmington received similar calls within the next half hour.

Automated bomb threats were also reported at Mispillion Elementary School in Milford and Sunnyside Elementary School in Smyrna earlier in the morning.

Florida

Storm Grove Middle School (Vero Beach): Students were bused to Sebastian River High School after someone sent an automated bomb threat to the middle school. Parents picked up their children from there.

Treasure Coast High School (Port St. Lucie): The school was evacuated after receiving a bomb threat shortly after 11 a.m. The school was searched, no explosives were found and students were allowed to return to class.

Iowa

Altoona: The school received a bomb threat at 11:54 a.m. saying bombs were inside the school. Students were relocated to a local church, where parents were able to pick them up. Buses will run Monday for parents who cannot pick up their children.

Valley High School (West Des Moines): The school received a bomb threat Monday afternoon. Students who could drive were allowed to go home while students who take the school bus were taken to a safe location until buses could take them home.

Tate High School (Iowa City): The school received an automated bomb threat. No other details were available.

Excelsior Middle School (Marion): The school was immediately evacuated after receiving a bomb threat about 12:30 p.m. The school dismissed students to parents and guardians.

Maine

Hall-Dale Middle School & High School (Farmingdale): Students were evacuated for about three hours after the school received a bomb threat Monday morning.

Maryland

Showell Elementary School (Berlin): The school was evacuated at about 11:25 a.m. because of an automated bomb threat.

Massachusetts

Willett Elementary School (Attleboro): The school was evacuated as a precaution after a bomb threat was called into the school. Students and staff returned to the building after police swept the school and deemed it safe.

Charlton Middle School: Students were evacuated just after 10 a.m. Monday and sent to Heritage School after the school received a bomb threat.

Dover Elementary School: Police swept the school after officials received a bomb threat.

Chase Street School (Somerset): The school received an automated bomb threat around 9:25 a.m. Students were evacuated. Around the same time schools in Barnstable, Wellfleet, Mashpee and Fall River received similar threats, which were all deemed unfounded.

Minnesota

Forest Lake Elementary School: The school was evacuated around 12:15 p.m. after a bomb threat was made by phone. Students were sent to Forest View Elementary School and were bused home from there.

Brooklyn Center Secondary School: The school was temporarily evacuated Monday after receiving a threatening phone call about 12:30 p.m. Police searched the building and students returned.

Montana

North Middle School (Great Falls): The school was evacuated after receiving a bomb threat. Students were bused to an elementary school, where parents could pick them up.

New Hampshire

Berlin Middle School: Students were sent to Berlin High School for lunch after the school received a bomb threat around 10:40 a.m.

Fuller Elementary School (Keene): The school was evacuated after receiving a bomb threat Monday morning.

Amherst Street Elementary School (Nashua): The school was evacuated after a bomb threat was called in. Students returned to class after police swept the school with a bomb sniffing dog and found nothing suspicious.

Portsmouth High School: The school was evacuated after it received a bomb threat. Police cleared the building and students were allowed back inside. No bomb was found.

Oregon

Irvington School (Portland): The school was evacuated about noon after receiving a threatening call. The school was searched and nothing was found.

Pennsylvania

Dallas School District: Bomb threats prompted the evacuation of Dallas Elementary School and Wycallis Elementary School on Monday. The schools later dismissed students early.

Utah

Murray High School: Students were evacuated and sent home for the day after a bomb threat was called into the school around noon.

Vermont

Northeast Elementary School (Rutland): The school was evacuated after staff received a bomb threat Monday morning. Students were taken to another school and parents were notified.

Washington

Long Beach Elementary: The school went into lockdown and called police after receiving a threatening call. The threat was deemed not credible.

Kessler Elementary (Longview): Parents were able to pick up their children at a church after 1:20 p.m.

York Elementary School (Vancouver): After the threat, students were taken to a back field area while the building was searched. Students returned to class after the building was cleared.

Wisconsin

Janet Berry Elementary School (Appleton): The school received a short, anonymous, automated phone call at 11:47 a.m. indicating a bomb would go off in the building. Staff and students stayed outside as police searched the school. They were allowed to return at 1:40 p.m.

Oakwood Elementary School (Oshkosh): The school received a threatening phone call around 11:50 a.m. School officials immediately implemented a "soft lockdown" and began evacuating the school, sending staff and 473 students to the Oshkosh YMCA. Parents were asked to pick up their children at the YMCA.

Edison Middle School (Green Bay): The school was locked down for about an hour Monday afternoon after receiving a threatening automated call at 11:40 a.m. Green Bay police expect federal investigators to take over any additional investigation.

Wilson Junior High School (Manitowoc): Police searched the school after officials received an automated call around 11:40 a.m. Students were not evacuated.

Northside Elementary School (Middleton): Students were evacuated and taken to a nearby church after the school received a called-in bomb threat around 11:45 a.m.

Pleasant Prairie Elementary School: Students and staff were evacuated after an 11:30 a.m. bomb threat. They were taken to a middle school, where parents could pick them up.

Appleton West High School: Parents received automated calls at home Monday evening from Principal Greg Hartjes saying, “Late this afternoon, we were made aware of a general threat to harm students at Appleton West High School.” He said police will search the school tomorrow morning before students enter and there will be an "additional police presence" at school on Tuesday. It is unclear whether this threat was related to the others.

Alison Dirr: 920-996-7266 or adirr@gannett.com; on Twitter @AlisonDirr; Reporters Jen Zettel and Ethan Safran contributed to this story.

Sources: The (London) Independent; KGET-TV, Bakersfield, Calif.; BNO News B.V., The Netherlands; The (Fort Collins, Colo.) Coloradoan; CBS4, Denver, Colo.; KKTV, Colorado Springs, Colo.; Delaware Online; TC (Florida) Palm; WPTV, West Palm Beach, Fla.; KCRG-TV9, Cedar Rapids, Iowa; The Des Moines (Iowa) Register; MaineToday Media; Delmarva (Md.) Media Group; FOX25, Dedham, Mass.; Thomas Willett Elementary School; The Great Falls (Mont.) Tribune; The (Minneapolis, Minn.) Star Tribune; WMUR-TV, Manchester, N.H.; New Hampshire (Manchester, N.H.) Union Leader; Seacoastonline.com; The (Keene) Sentinel; The (Portland, Ore.) Oregonian; The (Wilkes-Barre, Pa.) Times Leader; KSTU-FOX 13, Salt Lake City, Utah; WPTZ/WNNE, Plattsburgh, N.Y.; Ocean Beach School District; The (Longview, Wash.) Daily News; The (Appleton, Wis.) Post-Crescent; The Kenosha (Wis.) News; WMTV, Madison, Wis.; WLUK, Green Bay, Wis.; The Oshkosh (Wis.) Northwestern; The Green Bay (Wis.) Press-Gazette