In a letter dated Monday, the university officials said it experienced a cyber attack which targeted the personal records of both current and former employees, including student workers.
The hack exploited a vulnerability in software acquired by a vendor, university officials said.
Along with social security numbers, the files also included names, addresses and university ID numbers.
"The University took immediate corrective actions and is working closely with Federal Bureau of Investigation officials and Mandiant, a leading private computer security firm, on the issue," the letter reads.
It continued "The University continues to investigate the scope of the attack. While this forensic investigation is underway, the University is taking steps to protect itself from future cyberattacks."
Anyone with UDelNet IDs and passwords can check to see they are affected by this incident by using the IT Security Verification application on a special IT Security Response website.
In addition, those affected by the hack are being offered free credit monitoring.