The Genius Wars — Catherine Jinks

Boy-genius Cadel Piggot has a new name (Cadel Greenaius), a new family, and a new life. No more illegal hacking, no more false identities, and most of all, no more Prosper English. But when his best friend Sonja is attacked, it's up to him to figure out who was behind it. Before he knows it, Cadel is crossing oceans and continents, barrelling back into the depths of the criminal activity he thought he'd left behind, and coming face to face with Prosper English once again. Can Cadel track down Prosper before it's too late? And what rules will he have to break in the process?