The name of the polymorphic virus outbreak in 1991 was Tequila. The virus embedded itself in the hard drives of personal computers and changed the Master Boot Record. This made it impossible to reset the computer to get rid of system freezes and errors.
Like any polymorphic virus, Tequila constantly mutated its code every time it infected another computer or system property. As a result, antivirus software could not pinpoint the code structure and so could not clean the system of the infection. Tequila caused data loss because of the file-allocation errors that multiplied with each infection. The name was derived from tequila liquor; in 1991, it was the fastest-growing liquor in the United States.