Code: Lyoko is the code entered in any Tower to deactivate it. Once entered, it triggers a deactivation which stops X.A.N.A.'s attacks. Before Code Lyoko Evolution, Aelita was the only one who could enter this code. This code has been entered in every Tower at least once. The code is entered by entering the Tower, ascending to the upper platform, going to the terminal, and placing a palm on the terminal.
During Evolution, Ulrich, Yumi, and Odd also managed to deactivate the Tower because of the source codes they had. Even though X.A.N.A.'s spectres stole these codes and Odd lost over 70% of them and the Tower couldn't recognize who he was, he could still enter Code Lyoko.
Once the code is entered, all programs run by the Tower are stopped. If a Tower is used to materialize a monster, as soon as its deactivated, its Laser and the monster freeze in mid-air. If it is used to program an alteration of a sector, it goes back to normal. If the Tower is being used to regulate a Spectre, then the spectre disappears.
- The show was most likely named after the code, as in seasons 1-2, it was the main purpose of each episode to get to the activated tower so Aelita could enter the code LYOKO, and stop the attack.