Which of the following should be used with caution because of its ability to provide access to block level data instead of file level data?

CIFS (Common Internet File System) is a file-level protocol that presents shared directories and files, not raw block devices, so it does not provide block-level data access.

NFS (Network File System) is a file-level sharing protocol that abstracts storage behind a file system interface and does not expose block-level disk access.

iSCSI (Internet Small Computer Systems Interface) is a SAN protocol that presents raw block-level storage over IP networks, bypassing file system abstractions and allowing a connected host to read or write directly to disk blocks, which requires careful security controls because unauthorized access could expose or corrupt entire volumes.

NAS (Network Attached Storage) is a category of storage appliance that typically serves file-level access via protocols like NFS or CIFS, not block-level access like iSCSI.