Time Warner Inc. (TWX) on Monday said data on 600,000 current and former employees stored on computer back-up tapes was lost by an outside storage company and that the U.S. Secret Service (search) is investigating the incident.

Time Warner's data storage company, Boston-based Iron Mountain Inc. (IRM), lost the tapes during transport to a storage facility, Time Warner said.

The world's largest media company, which owns America Online, HBO and Warner Brothers studio, said the missing tapes contained data from Time Warner, including names and Social Security information on the employees. The tapes did not include personal data on Time Warner customers, it said.

A Time Warner spokeswoman said the data tapes included information dating back to 1986 on 600,000 employees, among them about 85,000 currently employed by Time Warner.

"While we have no evidence to suggest the information on the tapes has been accessed or misused, we are providing current and former employees with resources to monitor their credit reports while our investigation continues," Larry Cockell, Time Warner chief security officer officer said in a statement.

The spokeswoman said the data was shipped out of a Time Warner facility on March 22 to one of Iron Mountain's storage facilities, but never reached its destination. She did not provide other details on how the data was lost.

Time Warner's disclosure follows a string of other, high-profile security breaches in the United States.

In February, Bank of America said it had alerted federal investigators that computer backup tapes containing credit card records of U.S. senators and more than a million federal government employees were lost. It affected more than a third of the Pentagon's staff.

That same month, ChoicePoint Inc.(CPS), which provides identity verification services, said identity thieves gained access to a customer database of 145,000 profiles including Social Security numbers and credit reports. It took a pre-tax charge of $5.4 million to cover expenses related to the investigation.

Also, data broker LexisNexis (search), a division of Anglo-Dutch Reed Elsevier (search) reported in April identity thieves had gained access to 310,000 U.S. account holders' Social Security numbers, names, addresses and driver's license numbers in 59 break-in attempts over two years.

Iron Mountain's shares closed the day down 38 cents, or 1.28 percent, at $29.32 on the New York Stock Exchange, while Time Warner's shares were down a penny at $16.80.