Unionville-Chadds Ford School District officials closed CF Patton Middle School and Unionville High School Friday because of a threat posted on the social media app TikTok. According to Superintendent of Schools John Sanville, an investigation showed the threat to lack credibility.

In an email, Sanville said, “The police and district administrators spent the day interviewing students and reviewing the technology footprint of a number of people. Based on the findings of the investigation to date - it has been determined that it is safe to resume normal activities on campus.”

The incident follows reports of schools around the country concerned about similar threats of school shootings on Dec. 17. According to multiple reports, the threat came as a TikTok challenge in which students were to call in bomb threats.

“The sick stunt, which encourages kids to call in bomb threats, school shooting threats and other acts of violence, impacted schools across the nation, leading many to go remote for the day or bring in extra cops out of precaution,” reported the New York Post.

Nassau County Police Commissioner Patrick Ryder said, “‘All schools in the United States will be targeted on December 17.”

According to the Deseret News in Utah, school districts in Arizona, Connecticut, Illinois, Montana, New York, and Pennsylvania beefed up security. At the same time, those in California, Minnesota, Missouri, and Texas closed down Friday.

Yahoo News also reported, saying the threats were vague with no clear-cut target: “No specific schools or locations are mentioned in these viral threats, and law enforcement officials in several school districts across the country have said they have not found any credible threats to specific schools.”

According to Wikipedia, TikTok is a video-focused social networking service owned by a Chinese company, ByteDance. It hosts a variety of short-form user videos, from genres like pranks, stunts, tricks, jokes, dance, and entertainment with durations from 15 seconds to three minutes.