Species 6339 was the Borg designation for a humanoid, warp-capable species originating in Grid 124, Octant 22-theta. The Borg first encountered Species 6339 in 2371, and by 2375 over eleven billion individuals had been assimilated. Species 6339 vessels tended to be well-armed, the one encountered by USS Voyager in 2375 being equipped with twenty-two phaser cannons on its aft section alone.
In 2375, the Borg Collective detected one of Species 6339's last surviving shuttlecraft with thirteen individuals aboard, and a cube was sent to intercept it. However, unbeknownst to the Borg, Species 6339 had introduced a synthetic pathogen made to attack the programs in a Borg cube's vinculum. The virus brought chaos to the Borg's ordered hive consciousness, which led to the destruction of the cube.
The intentions of Species 6339 were that once another Borg ship had retrieved the vinculum from the destroyed cube, it would infect that ship, with the possibility of infecting dozens, perhaps hundreds of Borg vessels. (VOY: "Infinite Regress")
In the computer game Star Trek Online, this species is called the "Octanti". Remembering the near-extinction of their people nearly four decades before, the Octanti are dedicated to eradicating all Borg, making no distinction between the freed drones of the Cooperative and the main Collective.