Thousands of University of Wisconsin-Milwaukee students and staff could be at risk for identity theft.
The university sent letters to about 75,000 current and former employees and students Wednesday.
School officials said unauthorized people installed viruses on a university server in May. That server contained confidential information including names and Social Security numbers.
The security threat has been removed, and the school is working with local and federal authorities.
"If there's any good news in this, it's that there's no evidence that the Social Security numbers and the names in the database had actually been accessed by anyone,' UW-Milwaukee Vice Chancellor Tom Luljak said.
The school said a new online security system is now in place.
Copyright 2011 by WISN.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.