We employ private clouds on Amazon AWS, as well as encryption at rest and in transit. Here’s our security protocol:
https://sync.appfluence.com/static/security/security_overview.pdf
Uploaded files:
As with all cloud services, you should only use judgement when uploading files. For our system, the files are stored in private repository that requires login, but also have a randomly generated URL for sharing, very similar to Box or Dropbox.
If you delete a file from the system, no copies are stored in our system afterwards thus this file cannot be recovered.