Harvard evacuated four campus buildings Monday after an "unconfirmed bomb threat" via email.
The buildings included Sever, Emerson and Thayer halls, as well as the Science Center. Authorities say they're searching the buildings now.
The same four buildings were evacuated in 2013 after a bomb threat. That threat ended up being unfounded.
So far, Harvard officials say there is "nothing to substantiate the emailed threat."