Personal information for 600,000 current and former Time Warner employees has been lost, the company announced on Monday, potentially setting the stage for one of the largest cases yet of identity theft.

Time Warner said the mishap occurred on March 22, when data storage company Iron Mountain was transporting its backup tapes to a storage facility away from its offices. The company lost the tapes while in transit, said Kathy McKiernan, a Time Warner spokeswoman.

"The tapes were discovered missing on the same day they were picked up," McKiernan said. "We launched an investigation, and when we could not rule out foul play, we contacted the (US) Secret Service to investigate."

The Time Warner case is just the latest in a string of data theft cases to rock corporate America, from Bank of America to educational institutions such as the University of California at Berkeley.

Time Warner waited for more than a month before notifying current and past employees that their personal information may have been compromised.

"We didn't want to compromise the investigation," McKiernan said. "We determined we could notify people now without it impeding the investigation."

The media giant has set up an 800 number to answer past and current employees' questions and provide free credit monitoring for a year. A few days ago, the company began the process of encrypting its data.

To date, Time Warner says it has not received any notices of compromised personal information from current and former employees.