Keys cannot be hacked because:They regularly authenticate with the master server. If you do manage to get a hold of someone else's key, there will be an IP mismatch, causing an authentication failure. You can't really pretend to be using someone else's IP.
Servers cannot be hacked because:Everything server related is processed on the server. Things do not happen peer-to-peer.
The reason other shooters can be hacked is because of this peer-to-peer business.
Reason why damage hacks in MMOs and whatnot are possible is because they have to handle so many clients that they make the client process some of the actions, such as attacking and damage calculation.
The only way you could actually hack a server is to hack the computer itself. I'm sure there's something more sinister you could do rather than messing with their Blockland server if you pull this off.
Exploit found in the game and was fixed.
Memory editing.