We brought the box back with us and loaded it on our ship. However while in the warp, we encountered a humanoid-like creature and what appeared to be mechanical beetles. Hostile. And destructive. After retreating to the navigation helm and shutting bulkheads on our way, our techpriest was able to assess the damage: real-space engines were completely shut off and the warp engines were not far behind. We directed our psykers to send out SOS messages and asked our navigator to get us out of the warp as soon possible.
On our exit from the warp, we were intercepted by a Xenos ship — Eldar — and they informed us of what we had brought aboard: a Xenos species that I, and my colleagues, are unfamiliar with: the Necron. They are destructive and are capable of extreme regeneration. The box, which they called a sarcophagus, was destroyed with the Eldar equivalent of a melta-gun. That is the only way to destroy these monstrosities.