Anti Cheat are plugins added to minecraft servers to prevent players from hacking. When it comes to 2b2t, and several other anarchy servers, anti cheat has been implemented, however, usually to prevent extreme forms of hacking (flying, super speed, etc.) in order to provide a fair gameplay on the server, while less OP forms are usually accepted (Jesus, Kill Aura, etc.).
This page will explain the various forms of anti cheats implemented into 2b2t and their discrepancies and criticism.
NoCheatPlus (or simply NCP) has been the anti cheat implemented by Hause since the rise of server networks, plugins, and hacked clients way back during the full release days of minecraft. NCP can be administered by plugin companies such as Bukkit or, in 2b's case, Spigot.
The anticheat gained a lot of criticism by early players as they could no longer fly around or go insane speeds. People bashed Hause because of this and criticized that the anti cheat prevented true anarchy. Despite critics, Hause never removed the anticheat and it has been a part of the server until getting replaced by AAC.
The anticheat, over time, became somewhat praised by the community due to the fact that it prevents game breaking hacks but yet, for the most part, allows normal cheats like Kill Aura and things of that nature, allowing for some of the true anarchy to remain on the server.
Advanced Anti Cheat (or simply AAC) is another anti-cheat implemented into 2b2t by either Hause or Curtis . The anti cheat was implemented sometime in April 25th, 2017 and removed some time in Late April/Early May. It is administered solely by Spigot.
The anticheat was very criticized as players, like torogadude , have noted that the anticheat prevented many normal hacks, unlike NCP which to a degree did so but for the most part did not. Things like speed mining, kill aura, jesus, and slower speed hacks were known to kick players from the server.
The anticheat was rendering many of the most popular cheat clients on the server, such as Impact, Future, and Wurst, almost useless. Players had to be conscience about how much they use their regular hacks. In fact, even players without hacks were kicked due to horrendous lag. Hause was sent hundreds of emails on the day it was added in order for it to be removed. According to reports, 90 players, including no hack players, were kicked on the first day.
Revert to NCP (AAC's Fail)
Eventually, due to lots of critiscism and issues Hause eventually listened and reverted the anti cheat back to NCP. This was most likely due to an update in NCP and that the Apocalypse Exploit has been patched due to an IRC plugin that was implemented in order to fix the source code and tracks issues.
Revert Back to AAC
In early April of 2018 2b2t went back to AAC for unknown reasons. It is the the current anti-cheat on the server and doesn't seem to be leaving anytime soon, despite the various issues it has been causing and the many complaints about it.