Which of the following types of virus makes changes to a file system of a disk?

A master boot record virus infects the MBR sector to gain control at boot time, not the file system's directory or allocation table structures.

A stealth virus intercepts operating system calls to conceal its presence from scanners, and is defined by its evasion behavior rather than file system modification.

A cluster virus operates by altering directory entries or FAT pointers on disk so that executing any program causes the virus to run first. It targets the file system structure itself rather than directly modifying executable files, making every program access trigger the infection.

A macro virus embeds malicious code within document macros in files like Word or Excel documents, not within the disk's file system structure.