The University of California, Los Angeles alerted about 800,000 current and former students, faculty and staff on Tuesday that their names and certain personal information were exposed after a hacker broke into a campus computer system.
It was one of the largest such breaches involving a U.S. higher education institution.
The attacks on the database began in October 2005 and ended Nov. 21 of this year, when computer security technicians noticed suspicious database queries, according to a statement posted on a school Web site set up to answer questions about the theft.
Acting Chancellor Norman Abrams said in a letter posted on the site that while the database includes Social Security numbers, home addresses and birth dates, there was no evidence any data have been misused.
The letter suggests, however, that recipients contact credit reporting agencies and take steps to minimize the risk of potential identity theft. The database does not include driver's license numbers or credit card or banking information.
"We have a responsibility to safeguard personal information, an obligation that we take very seriously," Abrams wrote. "I deeply regret any concern or inconvenience this incident may cause you."
School representatives did not return calls for additional comment.
The breach is among the latest involving universities, financial institutions, private companies and government agencies. A stolen Veterans Affairs laptop contained information on 26.5 million veterans, and a hacker into the Nebraska child-support computer system may have gotten data on 300,000 people and 9,000 employers.
Security experts said the UCLA breach, in the sheer number of people affected, appeared to be among the largest at an American college or university.
"To my knowledge, it's absolutely one of the largest," Rodney Petersen, security task force coordinator for Educause, a nonprofit higher education association, told the Los Angeles Times.
Petersen said that in a Educause survey released in October, about a quarter of 400 colleges said that they had experienced a security incident in which confidential information was compromised during the previous 12 months, the newspaper reported.
In 2005, a database at the University of Southern California was hacked, exposing the records of 270,000 individuals.
This spring, Ohio University announced the first of what would be identified as five cases of data theft, affecting thousands of students, alumni and employees - including the president. About 173,000 Social Security numbers may have been stolen since March 2005, along with names, birth dates, medical records and home addresses.
Jim Davis, UCLA's chief information officer, said a computer trespasser used a program designed to exploit an undetected software flaw to bypass all security measures and gain access to the restricted database that contains information on about 800,000 current and former students, faculty and staff, as well as some student applicants and parents of students or applicants who applied for financial aid.
"In spite of our diligence, a sophisticated hacker found and exploited a subtle vulnerability in one of hundreds of applications," Davis said in the statement.
The university's investigation so far shows only that the hacker sought and obtained some of the Social Security numbers. But out of an abundance of caution, the school said, it was contacting everyone listed in the database.