The base files for Image backups are stored in the Local Storage folder as (.vhd) or (.vhdx) files. These files are not encrypted or compressed, which is what allows them to be restored more quickly than ones which are encrypted and compressed. While this advantage in recovery speed is helpful in a restore scenario, this may also leave the backup files open to modification.
We have observed circumstances in which the device containing the Local Storage folder was hit by malware (usually of the cryptolocker variety) and data on the base files was changed/corrupted. This prevented the software from restoring the image properly.
Our recommendation to prevent this from happening is to exercise strict user access control over the Local Storage folder. If you create a user account which is only used by the Backup Agent service and is the sole account to have access to the Local Storage folder, this should prevent these sort of occurrences from happening.