NEW YORK — Warning to Time Warner employees past and present: Your name, your Social Security number and where you live could be out there for all to see. And that goes for everyone from janitors to the conglom’s former topper Jerry Levin.

In one of the largest computer security breaches in recent times, Time Warner disclosed Monday that backup tapes containing nearly 20 years’ worth of personal data on 600,000 employees went mysteriously missing while being trucked to storage on March 22 by outside firm Iron Mountain.

Revelation came as the conglom began the daunting task of notifying present and former employees — a roster that dates all the way back to 1986 and includes Ted Turner, former AOL topper Steve Case, and former Warner Bros. toppers Bob Daly and Terry Semel.

An unarmored Iron Mountain truck picked up the small container of tapes at Time Warner Center headquarters in Gotham and then made a number of other stops before arriving at a storage facility in New Jersey — apparently sans the TW freight.

In a midday statement, TW said the matter is being investigated by the U.S. Secret Service, which cites identity theft as a growing black-market business. So far, there’s no evidence that the info on the TW tapes has been accessed or misused.

TW won’t say what personal data might be on the tapes, besides names and Social Security numbers. It keeps records on past employees because of retirement benefits and the like.

For security reasons, TW also wouldn’t comment on any particular person being on the tapes, or groups of people, such as top execs and board directors. It did say that certain non-employees who have provided services to the company might be on the tapes, but it wasn’t immediately clear who this applied to, or whether movie talent might fall in this category.

The case lands TW on a growing list of congloms facing security breaches in recent months, although those cases mostly dealt with customer, not employee, information.

Earlier this year, Iron Mountain was transporting — and then lost — Bank of America backup computer tapes of credit card records belonging to more than 1.2 million U.S. government employees. The tapes have never turned up; nor has there been any sign of identity theft.

Throughout the day Monday, the 85,000 current TW employees and 515,000 past employees received an email from corporate headquarters that will be followed by a letter.

“Time Warner takes the security of our employees’ personal information very seriously and we deeply regret that this incident has occurred. We are aggressively investigating this situation and are committed to staying in touch with you as the investigation unfolds,” TW senior VP and chief security officer Larry Cockell wrote in the email.

TW spokeswoman Kathy McKiernan said the conglom will begin encrypting all backup tapes.

A spokeswoman for Iron Mountain said the loss of the tapes was due to “human error,” noting that the driver has been terminated. Various scenarios include the container falling off the truck, or being delivered to the wrong party. Nothing, however, turned up when retracing the driver’s route.

TW and Iron Mountain brought in the Secret Service after they conducted an initial investigation and weren’t able to rule out foul play. So far, there is no evidence that the information has been accessed or misused.

TW said the vast majority of those exposed were actual employees, although there were some dependents and beneficiaries on the backup tapes.

Foreign employees aren’t likely to face the same risk, since they aren’t identified with a Social Security number, but they are being notified as a courtesy.

All U.S.-based employees, both past and present, will have free access to certain credit agencies for up to a year to make sure there is no suspicious activity. A toll-free number also has been set up in the U.S.

Time Warner said it and Iron Mountain were working closely with the Secret Service. TW said it had determined that going public wouldn’t hurt the investigation.