The Ktarian game was a single-player device worn over the ears and using a visual interface. The game displayed a grid pattern on which the player had to direct hovering disks into cone shaped objects over the course of multiple levels.
The first level consisted of only one disk and one cone, the second level had two cones and disks, and the third level had three of each. The game had at least 47 levels.
In 2368, Etana Jol introduced it to William T. Riker for the purpose of gaining control of Starfleet, while Riker was vacationing on Risa. Riker then unwittingly helped spread it aboard the USS Enterprise-D while en route to the Phoenix Cluster.
Wesley Crusher and Robin Lefler analyzed the game using a neurological behavior program in the engineering laboratory aboard the Enterprise and found that it rewarded a player's successful attempt by stimulating the pleasure center of the brain, creating a psychotropic addiction affecting higher reasoning and rendering that player completely submissive. It also activated the reticular formation and increased synaptic activity in the frontal lobe and prefrontal cortex. Etana's goal was apparently to covertly take control of the Federation by distributing the game throughout various ships, starting with the Enterprise and spreading out from there to other ships; to this end, she arranged for Riker to first hand the game over to Counsellor Deanna Troi and Doctor Beverly Crusher, who could then deactivate Data- the only crewmember completely immune to the game's influence- and continue the game's distribution unimpeded.
Fortunately, Wesley Crusher was able to deduce what had happened during a brief return visit to the ship, and was able to distract the attention of the brainwashed crew long enough to repair Data and give him time to work out a means of negating the game's influence. Data then used an optical burst from a modified palm beacon to counter the effect of the device on the bridge crew, subsequently programming the ship's internal lighting to broadcast the same frequency throughout the ship. (TNG: "The Game")