The Accunadden (Ah-q-nod-din) is a non-humanoid species from the Delta Quadrant. The species is extremely advanced, and has been known to be particularly hostile towards humans.
The species was discovered when, in 2372, the USS Freemont was dragged into the Delta quadrant by a Q. Since the Accunadden are an extremely territorial people, they immediately killed the entire crew of the ship, except one Ensign, cvscvs2. His report stated that they kept him alive so that humanity would always remember to never infringe on their territory again. They then forced the Q to send cvscvs2 back to the Alpha Quadrant, and subsequently killed the Q. The discovery of a race so powerful was shocking for most of humanity.
The next encounter with the species was in 2386. A rogue Accunadden vessel appeared near the USS Victory-D, then captained by the same cvscvs2 who had met them the first time. They claimed that, though the Victory was well within federation territory, cvscvs2 was again infringing on their territory. A battle ensued, with human weapons doing nothing against their shields, and one volley of their weapons nearly completely destroying the Victory. It seemed nearly hopeless when the scientist anajay2 discovered that the cure for Cancer, in gaseous form, could mingle with the aliens (who were also gaseous beings) and render them destroyed. This worked, and the Victory returned to Earth for repairs.
Since then, there have been no encounters with the species.
The Accunadden are a gaseous species, who somehow produce all the sounds that humans do. Their ships are round and nearly invincible, armed with devastating weapons that have never before been seen and impenetrable shields.
They have been known to be able to kill any species they come across, including the Borg and even the Q.
Not much else in known about the Accunadden.