Which season of Code Lyoko is this?

I used to watch it bakc when it came on Cartoon Network-Meguzi. But then I remember seeing it somewhere else and they were episodes I'd never seen before. I know it has to be around season 2 or 3, maybe 4, but all I remember is that there were these new techno, computerized-looking places in Lyoko that the characters had to get inside and figure out. Also they had new outfits while there, Aelida is de-virtualized and has been living with the gang at school, I think the guy (is it William?) that proably likes Yumi has also turned into a virtualized warrior on Lyoko, and at one point he was evil(?). I think that's about all I can remember, maybe some drama between Yumi and Ulrich but that's it. And I don't want to waste time looking for the specfic episodes I remember because I have no idea what season they're in. Help would be very very appreciated! (: