For six months, hackers had access to a server at the University of California, Berkeley, and stole personal information associated with as many as 160,000 students, alumni, and parents.

In an uncommonly thorough disclosure, a UC Berkeley spokeswoman said that the data breach began on Oct. 9, and lasted through April 9, when university IT personnel found messages left by the hackers and took action to close the breach.

The compromised server housed information from the UC Berkeley campus health services center and contained "Social Security numbers, health insurance information, and nontreatment medical information, such as immunization records and names of some of the physicians they may have seen for diagnoses or treatment," according to the spokeswoman.

It did not contain medical records such as patient diagnoses, treatments, or therapies.

On Friday, UC Berkeley began notifying students, alumni, and parents -- who may have personal information on student health service insurance forms -- that their personal information had been accessed without authorization. They also began notifying about 3,400 Mills College students who received health care through UC Berkeley.

The data in question dates back to 1999 for those affiliated with UC Berkeley and to 2001 for those affiliated with Mills College.

Shelton Waggener, UC Berkeley's associate vice chancellor for information technology and its CIO expressed regret for the incident and assured those affected that the university is committed to reducing its exposure to future attacks. He said that the university is working with law enforcement to investigate the incident.

The university has set up a 24-hour data theft hot line, 888-729-3301, to field inquiries and address concerns. Its Web site includes links to credit reporting agencies for requesting fraud alerts and obtaining credit reports, advisable steps to mitigate the risk of identity theft.

A university spokesperson did not immediate respond to a request for information about the method of attack. The incident FAQ document characterizes the attackers as "overseas criminals" and says they "were highly skilled and broke in using a number of different techniques." Further details may not emerge until the university completes its investigation.

Slavik Markovich, CTO of database security company Sentrigo, speculates that the hackers probably got in through a SQL injection attack on a public Web application.

He said it's not clear whether the hackers targeted UC Berkeley specifically or merely spotted a weakness in the university's network. "I think they just did some smart Google searches for certain errors and then started to target the application," he said.

Though he credits the university for having a prepared security response to the incident, he said IT personnel there could have done more to keep an eye on things. "The fact that it took them more than half a year to find out about the breach indicates that they do not have the correct policies and tools to monitor database access and behavior," he said.

He also said that the university should not have had databases containing information with different levels of sensitivity on the same server.

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