An attempt by the Ktarians in 2368 to take control of the Enterprise-D, and through it Starfleet, by spreading an addictive headset game that made its players suggestible.
The Ktarian game incident is shown in the Next Generation episode The Game. On leave at Risa, Riker is given a headset game by a woman named Etana Jol. It rewards the player with pleasure, and it also alters the brain so that players will do as the Ktarians wish.
Riker passes the device around the ship, and soon nearly everyone is playing. Beverly Crusher quietly shuts Data down, because an android cannot be affected. Wesley Crusher, visiting from Starfleet Academy, and Ensign Robin Lefler notice what is happening and are hunted through the ship until both are caught and forced to play.
Wesley has had time to repair Data in secret. Data arrives on the bridge and frees the crew with pulses of light from a palm beacon, and Jol's ship is taken in tow before the game can be distributed to other vessels.