On Linux and UNIX-like systems, files or directories that begin with a period (.) are considered hidden. These files do not appear by default when a user runs the ls command, unless explicitly instructed to show hidden files using ls -a.

Example:

File named .hiddenfile will not appear with a simple ls command.

To view it, use: ls -a

This is commonly used for configuration files (e.g., .bashrc, .profile) and also by attackers or malicious users who want to conceal their scripts or payloads.

Incorrect Options:

A. Exclamation mark (!) is used in shell history and command expansion, not for hiding files.

B. Underscore (_) is a valid filename character but does not hide files.

C. Tilde (~) represents the current user's home directory; not used for hiding.

Reference – CEH v13 Official Courseware:

Module 06: Malware Threats

Section: “Tactics to Hide Malware Files in the OS”

Lab: CEH Engage — Creating and Hiding Files in Linux

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