The University of Delaware said that confidential files containing personal information on 72,000 people were recently hacked.
The files include social security numbers, addresses and school ID numbers of past and current employees, including student employees.
School officials said the breach occurred when cyber criminals attacked a vulnerability in software provided by a vendor for one of the university's systems.
Officials sent letters yesterday to all those whose files were hacked and offered free credit monitoring through Kroll Advisory Solutions.
The administration said people can see if their files were attacked by accessing IT Security Verification application on a special IT Security Response website.
School officials also said they are working closely with Federal Bureau of Investigation officials and Mandiant, a computer security firm, over the issue. A forensic investigation is underway.