In a statement, Harvard said it had authorised "a very narrow, careful, and precise subject-line search" to protect confidential student information.

BBC: Harvard University file picture

"Consequently, with the approval of the dean of FAS (Faculty of Arts and Sciences) and the University General Counsel, and the support of the dean of Harvard College, a very narrow, careful, and precise subject-line search was conducted by the University's IT department, " they added.

CNN: Harvard apologizes after secret e-mail search