Client_Hack1337
This is a client sided add-on. When you press [keybind], it opens up a GUI with a list of online "hackers". You can attempt to "hack" one of them for EXP, which can increase your level. There is a 1/10 of a chance that it will notify the player you're hacking, and he can counter. If you are hacked from a counter, you LOSE exp and the player gets credited for your partial hack attempt.
It would be serverwide, so as long as that player is in Blockland, you can hack them.
It would work like this:
Each level adds 5 EXP to get to the next.
Hacking someone, depending on their level, can give you 1-3 EXP.
You can trade points earned from gaining levels to get hacker awareness and get a higher chance of being notified.