The tapes, which were misplaced by an outside data-storage company, contained company data including the names and Social Security numbers of U.S. employees and their dependents, the company said in a statement.
Time Warner Inc. did not immediately respond to requests for comment.
The U.S. Secret Service is investigating the incident, which occurred when the backup tapes were being transferred to a storage facility. Time Warner said it doesnt have any evidence that the data has been viewed or used improperly.
"We take the security of our employees personal information extremely seriously, and we deeply regret that this incident occurred," Larry Cockell, chief security officer at Time Warner, said in a statement.
Time Warner sent a letter to its employees explaining the loss and set up a toll-free number for employees to call with questions. The company also contacted major credit agencies and is paying for a one-year subscription to a credit-monitoring service.
The incident is similar to a number of recent mishaps.
In February, Bank of America N.A. said it lost backup tapes containing data and customer account information from the U.S. federal governments charge card program. Those tapes also were lost in transit to a storage facility.
In April, online brokerage Ameritrade Inc. acknowledged that it lost backup tapes in February with information on more than 200,000 clients. The tapes were damaged in transit by a shipping company, which Ameritrade declined to name.
Reports of data theft and data loss have increased since California passed its state Senate Bill 1386 in 2003. That law mandates that companies that maintain databases containing sensitive personal information disclose security breaches of those systems to any state residents whose information may have been exposed.
Many experts have suggested that the problem had been going on—unnoticed and unreported—before Californias Senate bill became law.
While the data on the lost Time Warner tapes is probably formatted to work with a proprietary system within the company, thieves still could get at the information, provided they could find the right machine to read the tape, said Richard Moulds, vice president of marketing at data-encryption hardware vendor nCipher Corp. Ltd.
"Companies spend millions of dollars protecting their [network] perimeter and on physical protections around their buildings, but its often these sorts of back doors that are the most dangerous, like somebody bribing the van driver," he said.
Moulds said data encryption can be a last line of defense for sensitive information if other protections fail.