Fractal encryption code
A fractal encryption code was a method by which the main computer of a Federation starship could be isolated, blocking an intruding force from taking control of all ship functions. 

Having traveled to the year 2063 from the year 2373, Lieutenant Commander Data of the  entered a fractal encryption code into the ship's computer to prevent takeover by a contingent of Borg drones. Stored in the android's neural net, the codes could neither be forceably removed nor assimilated by the Borg. Nevertheless, continuing their attempt to gain control of the Enterprise computer, the Borg Queen used unconventional means of persuasion to extract the codes. ()

de:Fraktaler Verschlüsselungscode
Computer technology