Brain

Brain is the industry standard name for a computer virus that was released in its first form in January 1986, and is considered to be the first computer virus for MS-DOS. It infects the boot sector of storage media formatted with the DOS File Allocation Table (FAT) file system.

Brain affects the IBM PC by replacing the boot sector of a floppy disk with a copy of the virus. The real boot sector is moved to another sector and marked as bad. Infected disks usually have five kilobytes of bad sectors. The disk label is usually changed to ©Brain, and the following text can be seen in infected boot sectors:

• Welcome to the Dungeon (c) 1986 Amjads (pvt) Ltd VIRUS_SHOE RECORD V9.0 Dedicated to the dynamic memories of millions of viruses who are no longer with us today - Thanks GOODNESS!!! BEWARE OF THE er..VIRUS : this program is catching program follows after these messages....$#@%$@!!

There are many minor and major variations to that version of the text. The virus slows down the floppy disk drive and makes seven kilobytes of memory unavailable to DOS. Brain was written by Amjad Farooq Alvi, who at the time lived in Chah Miran, near Lahore Railway Station, in Lahore, Pakistan. The brothers told TIME magazine they had written it to protect their medical software from piracy, and it was supposed to target copyright infringement only. 

The cryptic message "Welcome to the Dungeon", a safeguard and reference to an early programming forum on Dungeon BBS, appeared after a year because the brothers licensed a beta version of the code.