Here's the big question here: are mods/hacks detectable by a server so that it may detect modded clients at joining? The direct answer is: NO, even though it may appear to be detected.
Common misconceptions why people think that it may be detected:
They can detect versions and kick people of the wrong version. Can't they detect non-vanilla clients?Edit
Truth is, they can't. They can only tell if the client will be compatible with the server or not. This means that all clients in 1.8.x can join any server 1.8.x.
Also, the stuff about the "scanning the user's files" is a fake. The client does not have the ability to do that.
They disabled my radar in Rei's minimap!!!Edit
Well, Rei's minimap sends the information that its installed to the server. Then they provide the option for the server to disable it. NCP sends a MOTD to it, and the radar is off. (Its usually a string of color codes, so you may see blank lines when you join a server) This goes for some other mods too. However, its extremely easy for a coder to disable this. Some mod authors do not want their mods to be used as hacking, so they let the server disable it with plugins, even though it is bypassed easily.
If they can force Spigot clients, they can force vanilla clients.Edit
No. Spigot clients are special because they send a check to the server saying that they are Spigot. If a hacked client author does the same, they can do this too. Vanilla clients do not have the ability to send their mods to the server unless the mod specifically says so. So therefore, you cannot ban everyone with a non-vanilla client.
I turned on XRay and it showed all ores/ ESP is limited! Can they find out client-side render mods?Edit
No. It is not possible for someone to detect client side mods when you aren't being suspicious. But they can, however, show you false information about the world. Anti-XRay, for example, tells you that there are ores everywhere until the block is exposed to air. Anti-ESP hides entities you normally wouldn't see. While these do seem to "detect" XRay/ESP, it only limits it, not entirely blocking it. For a better "bypass" for xray, check if the ore is exposed to air before rendering it. This obviously takes up a lot of CPU, so you could just use CaveFinder.
An overview of Badlion and GCheatEdit
Badlion claims to detect some clients at login, and that there will be a point where clients are undetectable, and that hasn't come yet.
From reports, Badlion's kill aura detection methods.
-For kill aura: Detects click interval, and if there is a pattern (click every x milliseconds) then detect. Therefore, you need a Triggerbot with speed randomizer. There are also various "bugs" that can be used to detect the aura.
Badlion claims that it can detect clients at login! This is false, bans have shown that it has never happened and it WILL NEVER HAPPEN. Therefore, Badlion is just like any other anti-cheat system, using a kill aura detection system similar to Advanced Anti-Cheat's.
Speed of hitting randomizer
Rotation Speed Limit
Note: To detect if GCheat can really detect client sided mods, I enabled all client sided hacks with Wurst and joined it, and then played some games with all client sided mods. The account is not banned.
Now here's what Badlion says:
Claim 1: However, this hasn't happened yet - every hacked client out there IS DETECTABLE.
What would most players think?
They would panic, seeing that their Huzuni/Nodus could be detected at login. They then stop using the client, exactly what the admins want.
However, here's the truth:
All hacked clients are undetectable if you don't enable any hacks, and even if you do enable client sided mods are NOT detectable by GCheat, and require admin interference. If you see GCheat logs you see it only pick up only server sided mods (fly,speed) and the staff banning the users making it obvious that they used mods. (direct tunneling to ores/caves/players, etc)
2 Meanings of what it really means:
1. All hacked clients have mods that are detectable because it says that mods keep the "undetected" hacked clients down, these must be the "undetected" mods from what the logs have shown. If you fly, or show the server unusual behavior in movement or combat, you will get detected. Since almost every hacked clients has those hacks, every hacked client is detectable if you turn on the detectable hacks.
2. Mods can see your actions and tell if you used mods IF YOU MAKE IT OBVIOUS. Hacks like xray/cavefinder are the most easily detectable client side hack through a human spying on you.
It also turns into a common sense question. If GCheat detects every single client, why are there still mods banning users themselves? Its pretty obvious that GCheat is like any other anticheat, detecting unusual behavior in movement and combat and letting the mods do the rest.
It is the first of its kind that I have seen. It claims to come in two parts: server-side and client side! If it works successfully it might be able to pick up some hacks, if the client side scanner is strong enough. However, I don't know if it can pick up autoclickers or external programs, so...
And there are several ways to bypass client side plugins (this goes for every other MMO too!)
1. Fake indicator- Lies to the server that you have FairCraft installed, and tells fake data to the server. It might be achievable by listening to outbound traffic maybe?
Also I don't know if FairCraft checks it client side and then sends the result (clean or not) to the server, or it just collects the data and sends it to the server.
If it is checked client side (meaning it just sends "true", "false", but in a obfuscated way of course), it will be easy to bypass, because all you have to do is to return true (clean) to the server.
If it is checked server side (meaning that only client data is sent), it won't be as easy, but it will be easy to overload the server by sending too much data, logging in too fast, etc.
2. Lying to the client- Find a flaw to make FairCraft think your MC is clean.