University of Chicago calls off classes over online threat

Police officers patrol near the Main Quadrangles on the Hyde Park Campus of the University of Chicago on November 30, 2015.
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One of the nation's top universities called off classes on the first day students are due back from Thanksgiving holiday because of an online threat.

The University of Chicago said all classes and activities are canceled Monday after the FBI passed on an online threat of gun violence on the campus quad at 10 a.m. Monday.

The decision, which the FBI said was made by the university, could affect more than 30,000 students, faculty and staff who work on the Hyde Park campus south of downtown Chicago.

Students who live on campus are advised to stay indoors. The only facility that remains open is the medical center, which will treat patients but have added security.

The university was ranked No. 4 in the nation by U.S. News and World Report.