The personal information of approximately 15,000 New York City Transit Authority workers has been found on a compact disc inside a refurbished computer sold by a retailer.

Authorities are investigating how the CD found its way into the computer drive.

The Associated Press obtained a letter about the security breach from one of the affected employees.

The letter dated March 6 says there is no immediate indication that any of the information on the CD was copied. It says the New York Police Department is investigating.

An authority spokesman referred a reporter to the content of the letter for comment. It described the breach as a "singular event."

Employees and retirees have been told they are being provided with a year of free credit monitoring.

Explore further Personal data briefly exposed at NYC bike share

© 2014 The Associated Press. All rights reserved.