When you activate a code, it also becomes activated for the CPU. For example, if you enable the The Master Builders code, the CPU will also be capable of instant construction. This will cause you to receive mass attacks from the CPU, usually consisting of Dreadnoughts, Tiamats, or Monoliths depending on their race. The best way to protect from these mass attacks is to build a lot of LR Sensor Towers and build massive defenses. This include Ion Cannons, and building jump gates to protect your system, and mass Dreadnoughts.