Time Warner this week said it will "quickly" begin encrypting all data saved to backup tapes after 40 tapes with personal information on about 600,000 current and former employees were lost in transit to a storage facility.

The incident is among the biggest in a string of recent data-security mishaps that have also affected companies such as ChoicePoint, Bank of America and LexisNexis .

A shipping container that held the 40 data tapes was lost on March 22 during a routine shipment to an off-site facility by records management and storage firm Iron Mountain, Time Warner spokeswoman Kathy McKiernan said. She wouldn't provide more details.

However, McKiernan did say Time Warner is trying to convince officials at Boston-based Iron Mountain to change some of their handling procedures. She declined to expand on the status of those discussions.

The $42 billion New York-based media giant also said it has provided the affected employees with resources to monitor their credit reports. The lost tapes didn't include data about Time Warner customers, the company said.

Iron Mountain said it has had four incidents of tapes going missing this year. In late April, Ameritrade lost a data tape with the names of 200,000 clients. At the time, the company wouldn't disclose how the tapes were lost, but in an interview this week, Ameritrade CIO Asiff Hirji said that the tape fell off a conveyer belt in a shipping facility.

Hirji, who wouldn't identify the carrier, said that for "whatever reason," the shipper took "a bunch" of tapes out of its original secure box and placed them into another box. Sometime after that, the second box was damaged on the conveyer belt, and four tapes fell out.

"We found three," he said. "That other tape, I'm almost 100% sure, is somewhere in that facility -- probably in the rubbish bin. Or it has been destroyed in their lost and found. However, we can't take that chance. We have to assume it's lost and has gotten into nefarious hands. I'm not pointing fingers. I'm not deflecting blame. It's our responsibility."

Like Time Warner, Ameritrade is taking steps to protect the confidentiality of clients whose names and/or Social Security numbers were on the lost tape. For example, the company has stepped up monitoring to detect whether any identities have been compromised. So far, Hirji said, there has been no evidence of compromised data.

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