Last month's hack of a Harvard Graduate School of Arts and Sciences (GSAS) Web server may have compromised 10,000 sets of personal information from applicants and students, including 6,600 Social Security numbers and 500 Harvard ID numbers, the University said today.

Harvard began notifying those who may be affected today, after an investigation determined that the University could no longer stand by its initial conclusion that no personal information had been accessed and disseminated.

Officials said they had been unable to determine what if any information had been compromised, and so had decided to notify everyone who was potentially affected and give access to identity theft services free of charge.

"We're not going to be able to rule out that the individuals may have gotten access to this other information," said Daniel D. Moriarty, the University's chief information officer. "We've basically decided to proceed as a conservative measure with notifying the individuals who have been impacted and lining up the [identity theft] services for those individuals."

The University has contracted with the security firm Kroll Inc. to offer identity protection services, including credit reports and setting up fraud alerts.

—Staff writer Clifford M. Marks can be reached at cmarks@fas.harvard.edu

—Check TheCrimson.com for more updates.