Which of the following methods is not suitable for securing files?

Saving documents without a password is not a suitable method for securing files. When files are saved without a password, anyone with access to the computer or storage device can open and modify them. This means that sensitive or confidential information can be accessed and tampered with by unauthorized persons. Therefore, it is important to use passwords or other security measures to protect files from unauthorized access or modification. The other options mentioned - use of backup, use of antivirus, and proper labelling of storage devices - are all suitable methods for securing files, as they help to prevent data loss, protect against malware or viruses, and ensure that storage devices are properly identified and managed.