I figured out the checksum stuff, the client sents checksum for a few game specific files, and also each time for some specific actions. That the checksum is over 2000 byte was very confusing, but in reality this is all what they wanted, confuse =). For the specific game client files i added a checksum method server side, if the checksum do not match the player will simply be disconnected.
Basically, this means we have a base line of defence now for easy file hacking.
= 9780min (163h)