Blackwall

The Blackwall is a virtual wall that is said to keep free A.I.s from breaking through into the rest of the virtual world and wreaking havoc, possibly causing the end of the world along with it. To ensure this never happens, NetWatch works to keep others from destroying it. However, other groups, like the Voodoo Boys, believe the free A.I.s will help them conquer the virtual world and thus look for ways to destroy the Blackwall.

It's believed that NetWatch was only able to construct the Blackwall because the Free A.I.'s wanted to be left alone and in control of vast abandoned sections of the old net. The Blackwall often splits old network systems in half leading to stories of haunted data.

2077
It is revealed by various characters that the Blackwall is not an ICE but actually an AI masquerading as ICE whose job is to keep out rogue AIs it can identify. It is also referred to a band-aid solution due to the AI having the possibility to go rogue. The Voodoo Boys believe that this is inevitable and are willing to do anything to remove the Blackwall and win favors with the rogue AIs.

The image of Alt Cunningham reveals that the best way to survive beyond the blackwall is by assuming a human form to not turn into pure data, out of animalistic behavior.

Depending on the choices at the end of the game, either V or Johnny can agree to follow Alt Cunningham beyond the blackwall where they can fuse with her or roam free.

Trivia

 * It is possible to breach the Blackwall as evidenced by the AI of Alt Cunningham breaking free.
 * NightCorp used a rogue AI to brainwash and control their employees, resulting in a cyberpsycho incident.
 * Maelstrom were able to summon a rogue AI named "Lilith" through a ritual.

Mur noir