Updated

Energy Department officials on Monday began contacting 1,502 individuals by phone to inform them that their Social Security numbers and other information may have been compromised when a hacker gained entry to a department computer system eight months ago.

The workers, mostly contract employees, worked for the National Nuclear Security Administration, a semiautonomous agency within the department that deals with the government's nuclear weapons programs.

The computer theft occurred last September, but Energy Secretary Samuel Bodman and his deputy, Clay Sell, were not informed of it until last week. It was first publicly disclosed at a congressional hearing on Friday.

The department's National Nuclear Security Administration began notifying the workers by telephone on Monday, said DOE spokesman Craig Stevens.

The security breach occurred in a computer system at a service center in Albuquerque, N.M. The file that was compromised contained the names, Social Security numbers, security clearance levels and place of employment of 1,502 people working throughout the government nuclear weapons complex.

The system contained sensitive, but not classified material, department officials said. The NNSA also has a more secure computer system that includes nuclear weapons data and other classified material.

NNSA Administrator Linton Brooks told a House hearing on Friday that he learned of the security breach late last September, but did not inform either the two men to whom he reports — Energy Secretary Samuel Bodman or Deputy Secretary Clay Sell.

Bodman learned of the incident last week.

Brooks blamed a misunderstanding for the communications failure.

Rep. Joe Barton, R-Texas., chairman of the House Energy and Commerce Committee, on Friday said that Brooks, a former ambassador and nuclear arms control negotiator, should resign over the incident.

Stevens on Monday declined to speculate on Brooks' future. Bodman wants the department's inspector general's office to investigate the communications failure.