The macrobot controlling a macrovirus
The macrobot or "macro-nanite" was a Borg nanoprobe that was inadvertently activated in 2381 after a macrovirus knocked over one of the regeneration alcoves on the USS Voyager. The nanite assimilated the macrovirus, causing it to grow to macroscopic size.
Flying out of the cargo bay, the macrobot commandeered Voyager's systems and created numerous holograms of the Clown, Doctor Chaotica, and Michael Sullivan to subdue the onboard personnel. It then transferred itself onto an animatronic model of a hyper-evolved Human and made its way to the bridge, where it directed the ship on a course toward Cube 858779.
Just before Voyager reached its destination, Ensign Brad Boimler was able to distract the holograms while Ensign Sam Rutherford used "Neelix cheese" to shut down the ship's bio-neural systems. Rutherford then detached and contained the macrobot. (LD: "Twovix")