The Paxans were a xenophobic, isolationist, possibly energy-based species inhabiting a Class M planet orbiting a T-Tauri type star in the Ngame Nebula. The Paxans had advanced technology by the standards of 24th century Federation science, which could not counter it.
In order to conceal the Paxans' existence from intruders, they terraformed a protoplanet within the system. If an intruder were to come within their territory, they would be confronted with an apparent wormhole, in actual fact, an energy field, which would stun the ship's crew and place them in a state of biochemical stasis. The ship would then be transported out of their space. The intruder would then regain consciousness, assume the wormhole was responsible for their altered position, and depart.
In 2367, the USS Enterprise-D encountered the Paxans on two occasions. On the first occasion, the Paxans' normal attempts to escape detection failed, as Lieutenant Commander Data - an android - was immune to the energy field and was thus able to fend off the Paxan takeover. To escape destruction, Captain Jean-Luc Picard convinced the Paxans to erase the crew's memories of the incident, and ordered Data to never reveal the existence of the Paxans. However, clues left behind by the crew led them to return to the Paxan system, and once again into conflict with the species. Picard was able to convince the Paxans to give them a second chance, this time taking care to erase the clues that had stopped the deception working the first time around. (TNG: "Clues")