A refurbished computer that was sold was found to have the personal information of thousands of Metropolitan Transportation Authority workers, investigators say.
The information was stored on a CD that was found in the computer's drive.
The Transit Authority told employees there was no immediate indication any of the information was copied.
But employees and retirees will get a year of free credit monitoring.
The NYPD is investigating how the CD made its way into the drive.
A Transit Authority spokesman described the breach as a "singular event."