Parents from a Washtenaw County school received a letter from the principal informing them a threatening messages was posted on Twitter by a student at the school.
Dexter High School sent the letter to parents on Wednesday.
The letter said the school became aware on Tuesday night, that a student tweet contained inappropriate comments about the school and could be considered threatening.
Principal William Moran wrote, "Your child’s safety is our greatest priority. At no time have we felt that Dexter High School students were in danger of any harm."
The letter asked parents to talk to their children regarding the consequences of posting harmful messages on social media sites.
Moran said the school is working with authorities and an investigation is ongoing.
The school declined to release the name of the student involved.