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Pro Client-side encryption
Encryption is performed before content gets uploaded to the cloud.
With clients for Windows, Mac, iOS, Android, Windows Phone, and Blackberry.
Pro Free storage space (get additional space through bonuses)
5 GB, up to 16 GB with bonuses.
Because the software is proprietary, there's no way to review the security practices or really know how the software operates under the hood. As such it can be considered as not safe for sensitive information.