Code Lyoko, Season 4, Vol. 1

Four students, Yumi, Ulrich, Odd and Jeremy uncover the existence of a mysterious parallel universe, a virtual word called Lyoko. Both Earth and Lyoko are being threatened with destruction by a super virus, X.A.N.A, which has infected the Super Computer thats controls everything. Now the students, who are joined by Aetelia, a virtual being from Lyoko, must lead double lives: ordinary boarding school students on Earth and action heroes inside the digital world of Lyoko.