Around 40 school districts in Indiana canceled in-person classes Friday after receiving bomb threat emails.

Upon investigation, no suspicious or explosive devices were found in any schools, according to Indiana State Police. This comes after a wave of threats against Illinois schools earlier in the week. Those threats were also determined to be pranks.

False threats are becoming a bigger problem in schools. The trend, commonly referred to as “swatting” usually involves alerting authorities to a scene under false pretenses like a shooting or bomb. Even though the premise of swatting is that there is no actual danger, the incidents themselves have been known to turn deadly when police mistake individuals for assailants.

Authorities are still looking into the origin of the email.