SAN DIEGO -- Authorities Saturday were investigating a computer breach in which hackers may have accessed personal data belonging to about 33,000 people enrolled in the county's retirement plan.

"I am very concerned about this breach of security," county Supervisor Pam Slater-Price told The San Diego Union-Tribune. "At this time, we don't know the full extent of the breach. But if just one employee's personal information was accessed, that's one too many."

The targeted servers contain the names, Social Security numbers, addresses and dates of birth of current and former county employees, said Brian White, chief executive of the San Diego County Employees Retirement Association.

Letters advising the potentially affected employees to check with credit agencies and to notify the Social Security Administration were being mailed to members of the association, starting Saturday.

Current employees were notified by e-mail Friday, the Union-Tribune reported.

"We don't know whether this information was viewed or copied," White told the newspaper. "But we are letting all of our members know just in case so they can take steps to protect their personal information."

Members of the retirement association who have questions can call (619) 515-0130 or (888) 473-2372 or go to the association's Web site, www.sdcera.org, for more information.

The district attorney's Computer and Technology Crime High-Tech Response Team is investigating the breach, the Union-Tribune reported.

A state law that took effect in June 2003 requires people to be notified when their computerized personal data may have been compromised.

The breach of the retirement system serve was discovered July 21.

Last month, the University of California, San Diego, mailed similar letters to 3,300 students, staff and faculty after hackers got into a university server.