Harvard University gave the all-clear Monday afternoon for four campus buildings that were evacuated after unconfirmed reports of explosives.
Students were just showing up for final exams when the school, acting on an email threat, cleared out the Thayer Hall dormitory and three academic buildings. Several hours later, all were back open.
Harvard postponed its morning finals. Some students crowded into a nearby dining hall after the evacuation order, while others spilled onto the streets on a frigid day.
"It is a serious matter. We've seen in the past year with the Boston bombings that things like this are not supposed to be taken lightly," David Bicknell, a Harvard junior, told MSNBC. "It's just a sense of unease."
The four buildings are clustered together near Harvard Yard, at the historic center of campus. Harvard closed the yard to people with Harvard identification.
A White House official said that President Barack Obama had been briefed on the situation.
Last month, another Ivy League school, Yale University, was locked down for almost six hours after a report that an armed man was hearing to the school. Authorities later said it was believed to be a hoax.