Metro accidentally published the Social Security numbers of almost 4,700 past and present employees on its Web site last month, according to the transit agency.
The numbers were posted with a solicitation to companies for workers' compensation and risk management services. They were online from June 9 until June 25.
The employees received a letter warning them about the breach. Metro is providing them with a year of free credit report monitoring, $25,000 in identity theft insurance and counseling services.
"We deeply regret this incident and believe the likelihood of misuse of the information is low," said Metro Chief Safety Officer Ronald Keele. "However, we have taken additional steps to protect employee information by bolstering Internet security and requiring more checks and balances of materials before they are being released publicly."
The employees are being urged to watch their credit reports for signs of identity theft.
Officials are continuing to analyze the solicitation in case of other data breaches.
Metro officials said that according to the Identity Theft Resource Center, inadvertent online posting of personal and financial information is responsible for 15 percent of data breaches at businesses, governments and universities.