There are plugins that can detect custom clients, my server has one and sometimes people get insta banned.
Try to avoid servers using that plugin (/? to see if a server has that kind of plugin)
The plugins can detect modified clients though by tracing/checking how the clients sends data to the server and back.
This is also how the plugins work.
For example with a fastbreak hack, it sends different blockdata to the server then it would by breaking it normal. This allows them to check if you are hacking or not. However some people might think that lag can cause bans in this kind of cases, well no not exactly. Lag actually has influance on blockbreaking etc. But it still sends the same data to the server and back.
This can be used to pickup a lot of stuff like. Fly, Speedmine, Fastplace, Climb, No Fall, Fast Swing, Auto soup and a lot more.
There are plugins that can detect custom clients, my server has one and sometimes people get insta banned.
Try to avoid servers using that plugin (/? to see if a server has that kind of plugin)
I'm on a private client, last time I was on Hypixel, because my mouse kinda malfunctioned, so I have to turn on Kill Aura(Block+Range+Hit Speed) to prevent being killed, when I was in the middle of fixing my mouse, it insta-ban me for 30 days, so I learned my lesson, never turn you kill aura that has fast speeds on while you're AFK or smth else
Same, haven't been banned from Hypixel and I use a client.
Ive been hacking on Skywars on Hypixel for the last 4 Months with KillAura, Auto Armour, Speed Hack(Bunny hop), ESP, CHEST ESP, Tracers, Zoot, No Velocity, Sprint, Fullbright, Criticals(Mini jumps), ArmourBreaker, AntiHunger and AntiSuffocate. and also on servers like gotpvp aswell
-EDIT-
I use XIV Client and WURST
My best guess would be that it detects certain cheats not a modification in your game client. I noticed when cheating on an alt the other day, some hacks that are blocked on almost every server work on Hypixel. I'm pretty sure if you use things like NoSlowdown and Fly you can get banned easily. I got banned but it's because I was being blatant and using the FancyChat feature in Wurst to swear constantly.
Watch-Dog AC like detectes your movement before banning you, last time I use Lucid on Hypixel after getting unbanned, I turn on Kill aura, fly works flawlessly, but whn I stop and pick up smth on the ground, it bans me, I think a mod saw me and commanded watchdog ac to ban me for permanent
I've been on hypixel with wurst, using the arena brawl thingy, still don't know what that does, but yeh I played a few games with killaura and whatever, no ban.
If your using killaura and someone watchdog reports you it puts invis people around you and if you hit them you get banned so makesure killaura isnt on invisible people.
Alwin900 (04-15-2016)
i use kill aura and i turn on fly once in a while and im good
I've noticed some things about watchdog, how it detects cheats, and what hacks it does detect.
Killaura: This is detected by taking a nearby player and creating an npc of it that 360s your head to see if you hit it without looking at it. If so, you will be placed on the ban wave query.
Triggerbot: This is also detected I think by the same way it detects killaura.
Fly: I have never witnessed watchdog banning for flying. As long as you don't go up when flying and do it at fast speeds.
Velocity / Anti-KB: I have to discover how it detected it but I believe it damages you to see if you take knock back. I was banned for using this.
Autoclickers: I don't believe it can detect autoclickers.
There are something called ghost clients
I used multiple clients on hypixel and blatant hacked every single time and never got banned. Only time I actually got banned was when everyone in a sg lobby watchdog reported me and even then it was only a 7 day ban for "Blacklisted Mods" I made an appeal and instantly got unbanned and carried on hacking.
I used Wurst, XIV, Tomato, Sallos, Huzuni and a bunch others and I turned on every hack possible.