In this article in De Morgen Eddy Willems thinks that he or the group is from Belgium because he has been attacking Belgian targets lately. He thinks they are frenchspeaking.
Rex Mundi discovered Belgium. He was hacking in France, Netherlands and some other countries while by chance he discovered that the state of internetsecurity was so bad here that it was a piece of cake to hack websites of some specific sectors who have no oversight at all and where everybody can do on the web whatever he does well or bad and nearly nobody cares a bit about their responsabilities and the consequences because there is nobody who has the power or wants to effectively use his authority voluntarily to impose norms, audits and punishments.
I could be wrong because Rex Mundi seems to have learned a lot from the mistakes the Lulzsec people made and the fact that he is still out there hacking and changing the way he is operating seems to confirm this. Rex Mundi is a ghost.
Rex Mundi will never be caught if there is no dedicated international team that hunts him down like all other big or important hackers and cybercrime groups have been hunted down. This was never done by one country or one operation but by a coordinated international team with all the necessary resources, judicial powers and evidence.
Otherwise we they will never find Rex Mundi
I am not Rex Mundi and even not part of it. Never was.
But I don't understand what all that grandstanding about the digital Interpol is while here is one example of one experienced hackers ransacking Belgium for the moment but ready to go back to whatever countries he tried out first.