A tsunami of emailed bomb threats is prompting closures at hospitals, schools, public transit agencies, and businesses across the US and Canada.

Word of the emails surfaced Thursday morning in tweets such as this one:

So I actually just got a bomb threat in my work email today ordering me to send the person $20,000 via bitcoin or they will blow up my place of work.... 2018 is wild pic.twitter.com/sn0vVLwe6v — Ryan William Grant (@TheeRyanGrant) December 13, 2018

And this one:

A truly vile twist on extortion spam: bomb threats. An incredibly good way to attract the attention of the FBI, though ¯\_(ツ)_/¯ (Check that closing disclaimer!) pic.twitter.com/ShX1bP6Tee — sammy (@0x736A) December 13, 2018

The emails warn that explosives have been planted in the recipient’s premises and that they will detonate by the end of the day unless the target pays $20,000 in bitcoin. By late Thursday afternoon, Sammy, the email security researcher who sent one of the tweets above, told Ars she and other researchers estimated more than 100,000 such emails had been received. A large percentage of the emails, she said, used unique wallet addresses and variations on the sender’s name as well as the type of explosive materials.

The emails prompted closures all around the country, including:

Disruptions to the San Francisco Municipal Railway’s bus lines and evacuations of the Jewish Community Center of San Francisco and San Francisco Fire Credit Union headquarters, according to the San Francisco Chronicle.

Multiple hospital and business closures in Chicago, as reported by the city’s ABC 7.

Building closures and school lockdowns in Tampa, Florida, the Tampa Bay Times reported.

So far, there are no reports of any explosive materials being found. Police throughout the country said the threats are hoaxes:

At this time, it appears that these threats are meant to cause disruption and/or obtain money. We’ll respond to each call regarding these emails to conduct a search but we wanted to share this information so the credibility of these threats can be assessed as likely NOT CREDIBLE. — NYPD NEWS (@NYPDnews) December 13, 2018

It seems unlikely the person or people responsible for the wave of emails expect to make money from the stunt. After all, the average person will need a day or more just to figure out how to use bitcoin. And even people who hold bitcoin aren’t likely to make a $20,000 payment without first calling the police.

A more plausible motivation is to create disruptions at an unprecedented scale or at least to experiment with such mass disruptions. Unfortunately, the hoaxers seem to have succeeded.