Virus - Brain (1986)

`Brain' was the first virus to hit computers running Microsoft's then popular operating system DOS. The virus was written by two Pakistani brothers, Basit Farooq Alvi and his brother Amjad Farooq Alvi and left the phone number of their computer repair shop. 

A boot-sector virus, Brain infected the boot records of 360K floppy disks. The virus would fill unused space on the floppy disk so that it could not be used. The first "stealth" virus, it hid itself from any detection by disguising the infected space on the disk. Due to its partial non-destructiveness, Brain often went undetected as many times users paid little attention to the slow speed of floppy disk access.

The virus was also known as Lahore, Pakistani and Pakistani Brain. BusinessWeek magazine called the virus the Pakistani flu. The brothers told TIME magazine they had written it to protect their medical software from piracy and it was supposed to target copyright infringers only.