The Unternet is a virtual world/platform within which users can live out their innermost desires without consequence. It's presence was first revealed to the hero community during the Final Crisis when an informer within the Secret Society of Supervillains offered the Unternet as a communication line currently uncontrolled by Darkseid.
Developed by Doctor Sivana and produced by Darkseid during his control of Intergang as Boss Darkside, the Unternet was designed to slowly corrupt its users by influencing and corrupting their desires and destroying their inhibitions.
Following Darkseid's defeat during the Final Crisis, the Calculator maintained control of the platform to be used as a secure networking location for criminals and supervillains to communicate with each other across the globe.
Calculator would eventually lose control of the Unternet over to businessman Viktor Mikalek, who began using it as a training platform for supervillains by including virtual simulations of real-world heroes for users to attack and kill.
Upon its discovery by the hero community, Red Robin attempted to secretly gain control of the Unternet in order to eavsdrop on supervillain communications, however, upon learning of its ability to corrupt and his own failure in securing control of the platform, he attempted to destroy the virtual platform altogether and disrupt the villains' communication hub.