Which of the following is the first computer virus that was used to infect the boot sector of storage media formatted with the DOS File Allocation Table (FAT) file system?

Melissa (1999) was a macro virus distributed via Microsoft Word documents and email, and had nothing to do with boot sector infection on FAT file systems.

Tequila (1991) was a polymorphic file infector targeting .COM and .EXE files, not the first boot sector virus, and appeared five years after Brain.

Brain is historically documented as the first IBM PC-compatible virus, specifically designed to infect the boot sector of floppy disks formatted with the DOS FAT file system. It worked by replacing the boot sector with its own code and hiding the original boot sector elsewhere on the disk. Released in 1986, it predates all other choices by several years, making it the correct answer to this historical question.

ILOVEYOU (2000) was a VBScript worm that propagated via email attachments and overwrote files, not a boot sector virus and not from the DOS FAT era.