So that the server can block/allow connection for unidentified or identified clients. If the clients are working under lisences, the server can read lisences from the providor of the client. If it detects it, it investigates and if so, kills and bans the player. Ok, what about if the server doesn't have a plugin that already does this, what about a plugin that is always detecting for irregular behaviour.
Maybe if the player isn't hacking or is lagging then maybe you can add that when the anti-hack client realises that when the player stops lagging, it stops using the hacks against the player. This is my idea, if you have any questions, ideas or opinions, leave them below.
Now I realise that they may be so problems with this: if either player lags or the hit registration is off but I am sure there is a way to prevent this. The server might not be happy with this but if the program is made so that the player using it can't trigger the "hacks" themselves, I don't see the problem with it. By using this client, you can beat them at their own game.
I know this isn't exactly ethical or maybe not even possible but hackers deserve to be beaten or banned. It then continues to detect for irregular behaviour from interactions with other players. After either, the player is been unable to defeat the hacker or the hacker has been killed, the 'hacks' on your own client stop. When this client detects this, it triggers it's own killaura, knock back, regen and more so that the actual hacker can be killed. For example, when you are fighting someone, it is detecting whether they are having no knock back, getting more hits than possible or not taking damage. What if you could make a client that is always detecting irregular behaviour. Since I have no coding knowledge somebody else would have to take this idea and make it. But could there be such a thing as an anti-hacking client. You can trigger keys to auto-fight, forcefield, regen, no knock back and more. Hackers are not welcome on the server, yet there are hardly any moderators on around the clock so I had an idea.