A teacher's lesson on Islam in Virginia's Bible Belt has sparked thousands of angry emails and social media postings.

Superintendent Eric Bond said in a message to parents and employees Friday that some of the messages "posed a risk of harm to school officials" and threatened protests.

As a precaution, the estimated 10,000 students in Augusta County's public school system got a one-day jump on the Christmas break. The cancellation of classes Friday also wiped out a holiday concert and weekend sporting events.

The lesson at Riverheads High School involved practicing calligraphy and writing a statement in Arabic.

Augusta County Sheriff Randall D. Fisher said security has been assigned to Bond, the school's principal and teacher Cheryl LaPorte, who created the lesson.