Hackers have broken into a top U.S. military laboratory possibly leaking personal information about visitors, the lab said Friday.

The sophisticated attacks were made against the Oak Ridge National Laboratory (ORNL) in Tennessee and Los Alamos National Laboratory in New Mexico lab director Thom Mason wrote in a memo posted to the U.S. Department of Energy facility.

Information that may have been accessed by hackers includes a database of names, Social Security numbers and the birth dates of every lab visitor between 1990 and 2004, the memo said. However no classified data stored on the lab's supercomputer was compromised, Mason said.

While there is no evidence that the stolen information has been used, the Laboratory deeply regrets the inconvenience caused by this event, mason wrote

The form of the attack is called fishing, which involves sending unaware users official looking e-mails with attachments. Users in the lab attacks were told in the messages to open the attachments. Once opened the attachments enabled the attackers to enter the database of information.

Those who may have had their information compromised were advised to place a fraud alert on their credit a major U.S. credit rating agency.

The lab is located about 25 miles west of Knoxville.

Tennessee Hacking