An 18-year-old Urbana High School student was taken into custody Monday on a felony charge after police accused her of writing a threatening message on the stall door of a bathroom at the school.

Police determined the message, which threatened that there would be an explosion in the building at 500 Washington Ave., was “a hoax.”

Brianne Castle of Urbana was arrested on suspicion of inducing panic, a fourth-degree felony, according to the Urbana Police Department. She was booked into the Tri County Regional Jail where she has since been released.

Police said Castle was responsible for writing a threatening message in the women’s bathroom at the school. The message, written in colored permanent marker, indicated there would be an explosion at the school at a specifically designated time, according to the police department.

Police said officers were already at the school on an unrelated manner.

The message was discovered early Monday afternoon after a student asked one of the officers if they were in the building because of the threat, according to the police department.

Cox Media Group received an anonymous tip via email early Monday afternoon that the high school was on lockdown and that “students were told to go to the back of the classroom.” According to the tip, a student texted her father, who was at work, and told him about the lockdown.

Urbana City Schools Superintendent Charles Thiel said the building was searched by school staff and police officers, who found “no credible evidence of a continuing threat.” The lockdown lasted approximately 35 minutes, he said.