A computer hard drive containing Social Security numbers and other personal information on nearly 1,300 California National Guard troops deployed to the U.S.-Mexico border has apparently been stolen.

The hard drive was reported missing Feb. 23 from the Guard's border mission headquarters inside San Diego Naval Base, said California National Guard spokesman Lt. Col. Jon Siepmann. It contains home addresses, birth dates and other identifying information for all soldiers serving long-term assignments on the border.

The Guard notified the soldiers Feb. 28 that their information had been compromised. It advised them to begin checking credit statements and take other protective measures.

The Guard has turned the investigation over to the Navy's Criminal Investigative Division, Siepmann said.

"Our theory right now — and obviously this is an investigation that's ongoing — is that it was taken for its intrinsic value," Siepmann said of the computer. "It cost us about $450."

Investigators are focusing on whether a Guard member stole the drive, Siepmann said. It was inside a building controlled by keycard access, but about 20 Guardsmen have regular access to the room.