All Cloudzy backups are stored within your own AWS account. Cloudzy does not have access to any data or files within the backups that are created using the service.
EC2 backups are stored as block device snapshots on S3. All snapshots are incremental. Only the blocks on the device that have changed after your most recent snapshot are saved. This reduces the time required to create the snapshot and saves on storage costs. Amazon S3 maintains multiple copies the backup snapshots on systems that are designed for 99.999999999% durability.
If your instances uses encrypted EBS volumes, then your snapshot backups are also encrypted.
For more information see:
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EBSSnapshots.html