CARBONDALE, Ill. (CBS) — Three residence halls at Southern Illinois University at Carbondale were evacuated overnight, following a bomb threat.

The university issued a campus alert at approximately 11 p.m. Thursday. The evacuation involved the Brush Towers dorms, which are composed of two 17-story towers named the Mae Smith, Neely and Schneider halls.

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Hundreds of students were told to leave their dorm rooms and were directed to the Recreation Center, Student Center and Morris Library.

The towers were inspected by police using bomb sniffing dogs.

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When nothing was found, students were allowed to return to the dorms around 1:15 a.m. Friday.

The scare came one day after SIU received a threat in the mail that caused campus alert Wednesday. The FBI is investigating that threat.

The Southern Illinoisan newspaper reported the nature of the mailed threat was not reported by law enforcement officials or university administrators. Classes on Wednesday went on as scheduled, but a campus wide alert was issued.

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An FBI spokesman said it did not appear that the SIU threat was related to other threats at campuses in several states, or to recent unrest in the Middle East and North Africa.