BIRMINGHAN, Mich. (WWJ) – Schools officials in Birmingham say someone hacked into an account and left a vague threat against Derby Middle School.

Speaking to WWJ Newsradio 950 on Thursday, Superintendent Daniel Nerad said no one has been hurt, but police are on campus and they are investigating.

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“We don’t believe that this a credible threat,” he stressed, “but until it is fully investigated we must treat it as something very serious. So the way we’re treating this today is having a significant police presence on the school campus.”

Nerad said classes remain in session, but parents may pick up their children early if they wish.

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“I’ve talked to many parents at the school today and, you know, they’re concerned, rightfully so. And what I’ve told them is it’s really something I want you to decide in terms of what you’re comfortable with; in terms of having your child in school or not,” he added.

Nerad said while a number of students had left before noon, most children stayed in school.

Police and school officials are not releasing any details about the nature of the threat at this time.

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[MEANWHILE: Plymouth-Canton High Schools Dismiss Early As Police Investigate Threat]