Not sure, need to look into it.

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Versioned Wallet Backups

The last 50 updates to a wallets are now stored remotely on Amazon S3. This is in addition to the latest wallet being synchronously stored on all 4 of blockchain.info's servers and offsite database dumps taken every 24 hours. Wallets on S3 are encrypted with the users password, second password, our secret and encrypted by amazon itself.

In addition to providing much improved redundancy, should any mistakes be made (for example the wrong private key is deleted) backups can now be restored easily from S3 in the [Import / Export] tab.