Air, sea and land communications are crippled. Assets are frozen. Salary, welfare and social security payments cease. International transactions are suspended. Despite safeguards, stock markets crash, triggering trillion-dollar lawsuits.
Food riots erupt.
Civil disorder follows. Interconnected by a vast and now dormant electronic matrix, the world is in disarray. Computers are basically stupid. They follow instructions that humans program them to do. If the instructions make no sense to the computer, strange things can happen.