Jeremy, Odd and others in “Unfinished Business”

It's pretty obvious.

There he goes again.

You see, when Lyoko was destroyed, Hopper wasn't spread all over the network. He managed to escape.

He disappeared on purpose, is that it?

That's right. To get away from X.A.N.A. which is why he's constantly trying to throw Aelita into the digital sea all the time. He knows that's the only way to get Hopper to come out of hiding.

Ulrich

In order to destroy him.

As long as my father is alive, he'll always be a big threat to X.A.N.A.

And our friend X.A.N.A. knows it.