The Undernet is a thematic end-of-game area in the MegaMan Battle Network series. It is a hangout and home for criminal NetNavis that consider most "Surface" NetNavis to be weak and spineless. Rarely, denizens of the Undernet will interact with the Overworld Cyber Network, usually to deliver a message, or to carry out an order. The Undernet is dark, and generally characterized by faded colors and the "TV Snow" static that symbolizes bad reception for an electronic device.
The Undernet was originally a creation of SciLab, designed to hold the powerful program known as Giga Freeze. Due to it's remote nature and lack of constant interfacing, it became popular as a hiding place, and then a home for Criminal NetNavis. It is considered taboo by many regular NetNavis. It is also the home of Bass.EXE and Serenade.EXE, who frequent different parts of the abyssal area. The Undernet has several deeper ares connected to it. In Mega Man battle Network 3, it connects to the eerily peaceful Secret Area. In Mega Man Battle Network 4, it connects to a world of darkness called Murkland, also known as the "Black Earth". In MegaMan Battle Network 5, a Mr. Prog opens a portal to Nebula Area in the UnderNet. In Mega Man Battle Network 6, it connects to a shadowed land known simply as the Graveyard. The Graveyard, as the name states, is the realm where all remaining data of deleted Navis are stored in graves.