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From the Wiki:
Closed Shell Syndrome is a disease in Ghost in the Shell: Stand Alone Complex. Closed Shell Syndrome is a form of cyberbrain-induced autism (not to be confused with the "Autistic Mode" used by the cyberbrains of soldiers, which merely fully shuts down their networking functions). It occurs when users who are too compatible with cyberbrain technology eventually shut themselves off from the outside world to avoid harming others or themselves by forcibly accessing their cyberbrains. CSS patients tend to be savants with extremely high computer skills, and are often used to build and deconstruct network barriers.