Antioch University says one of its computer systems that contained personal information on about 70,000 people was breached by an unauthorized intruder three times last year.
The university says there is no conclusive evidence any personal information has been stolen but law enforcement officials are investigating.
The breached system contains names, Social Security numbers, academic records and payroll documents for current and former students, applicants and employees going back to 1996.
Antioch University has campuses in Yellow Springs, Ohio; Seattle; Los Angeles and Santa Barbara, California; and Keene, New Hampshire.
The breaches occurred on June 9, June 10 and Oct. 11.
The university said that when it became aware of the intrusion, it took the server offline and shut down the area that enabled the intrusion to take place. The school said it is reviewing computer security to make sure there are no other vulnerable areas.
"No conclusive evidence has been found that the intruder actually misappropriated any personal information," said Bill Marshall, chief information officer. "However, authorities are continuing to analyze all available evidence to determine the extent of the intrusion."
The university said it is contacting by mail people whose information could have been exposed.
Antioch College in this southwest Ohio village, the university's flagship campus, plans to temporarily close in June because of declining enrollment — now 200 — and heavy dependence on tuition and a small endowment. Officials hope to reopen the school by 2012.