Again, sneaking in to clear this point up, as a few people seem to be a little confused
Kalin doesn't hack into the mainframe in the true sense of the word All he does is steal Chatton's login credentials and uses those to set up a new user account for himself with administrator privileges. We know from the text that he's far more IT-savvy than most kids his age, so once he's into the system via Chatton's account, it's perfectly plausible that he could create a new user account for himself.
Kata obeyed. Stepping forward until the dark background of the screen didn't reflect his face, taking care to keep his back to the security camera in the room, he flicked his eyes down, watching not the screen but the scientist's fingers on the keyboard, watching the word they spelled out.Crossing over to the computer, he tapped in Chatton's name and password, then started to explore. The man had administrator privileges. That was even better; now there was far less risk of anyone catching him snooping.
[...]
He accessed the database and set up a completely new account. Name Taylork, password Renfield. There was a certain grim justice to that which he thought the scientist would have appreciated.
Hope that clarifies a little *sneaks back out again*