A computer-dwelling entity downloaded from a Gamma Quadrant probe, nicknamed Pup by Miles O'Brien, which causes faults across Deep Space 9 to keep his attention.
Pup is the name Miles O'Brien gives to a software entity that settles in the computer of Deep Space 9 in The Forsaken. It arrives when the crew download the records of an unknown probe that has come through the wormhole from the Gamma Quadrant.
At first the station's stubborn Cardassian computer becomes strangely helpful. O'Brien then sees that faults break out whenever he tries to leave his work, and concludes that something like an abandoned puppy has followed him home and wants company. Attempts to send it back to the probe only make it more troublesome, and its interference leads to a plasma fire that traps Bashir and a party of visiting ambassadors in a corridor.
O'Brien solves the problem by adopting it. He writes a subprogramme, which he calls a doghouse, where the entity can live happily inside the station's systems.