Trolling

Griefing is the act of destroying other people's creations on a multiplayer Creative or Survival server. It is frowned upon by the majority of Minecraft users because it ruins many hours of work, and makes maps untidy. In best case scenarios, the griefer is forced from the server quickly and their damage is trivial to repair. At worst, griefing can destroy an entire server.

The most effective way to fight griefers is to have the Admin or an Op check up on what all the players are doing regularly by using the teleport op command. If a griefer is found, a /kick or /ban command is usually used. Sometimes, a griefer can change their name to evade the ban. If this occurs, an /ipban is used on the perpetrator's ip address. Sometimes, a griefer can get by this command as well by using a proxy to change their ip. When this is the case, it is probably best to shut down the server for a while so the griefer gets bored and moves on.

A way to stop griefers from entering a server while no Ops are on is to use Spawn Jails. If built properly, this will ensure no player will be able to enter the map unless an op lets them. Some players consider this a rude practise however.

Possible Survival Griefing
See here.

Random Destruction
Random destruction is when a griefer destroys random blocks, putting holes in walls and other structures, making them look broken and messy. A griefer can also target an entire structure, working to destroy it completely. If no Ops are present, the way to combat this is to repair the damage by hand. Continue repairing until the griefer gets bored and leaves.

Random Construction
The opposite of random destruction, random construction occurs when a griefer creates random blocks on constructions and anything else on a map, making it look messy. The way to combat this is to just remove the extra blocks. Again, continue this until the griefer gets bored and leaves. This type of griefing may not seem as bad as the first, but it can be just as annoying to builders, and as fun to the griefers. Often griefers both destroy and create blocks in their quest to gain enjoyment at the expense of others.

Water Flood
A Water Flood is only applicable to Creative mode, as it uses infinite water. In Alpha, an attempted flood is very easy to fix. A water flood occurs when a griefer causes water to spill onto the level, often flooding a good part of it. Normally floods can only occur under sea level as that is the highest water can go, but it is possible to have water higher up using Map Editing. A way to combat this is to make sure Ops safe guard any potentially dangerous bodies of water with Bedrock to prevent the water escaping. Floods can also be prevented by using Sponges, which do not allow water to flow 2 blocks in any direction from the sponge. Hiding sponges in corners of rooms and other structures can prevent the structure from being flooded at all, possibly. If a small and located flood happens, the quickest solution is to gather some helpers and use Sponges to completely remove any water, then remove the sponges. Make sure no water is left behind when removing the sponges however, because 1 block of water can restart the flood again. If the flood is more large scale, have the Admin remove all the water using a Map Editor such as Omen by replacing all the water blocks with air.

Another danger of this kind of griefing is the massive lag that occurs on the server during a large water flood. If the flood is large enough, all players will be kicked out of the server due to the lag.

Lava Flood
Similar to a Water Flood, a Lava floods the area with lava instead of water. Lava spreads far slowly than water does, so if the flood is caught quickly, it can be stopped before it causes real damage. If no lava has been placed through map editing, floods can only occur deep underground where lava is. However, like water, if lava has been placed high on the map, make sure any pools of lava are protected from flooding by Bedrock. Lava floods can be very dangerous in Alpha mode for lava will set certain blocks on fire, like Wood and Trees. Lava cannot be removed with Sponges like water can, so the only way to remove it on a Creative server is to use a map editor like Omen.

Offensive Constructions
Some griefers grief by writing rude words or drawing offensive symbols everywhere. It's often generally harmless fun, but if a player finds it offensive they can destroy the offending problem, hence the griefer has become the griefed. This is far less of a problem than the others, for some servers are lenient and won't care about what the griefer writes or draws.

Flattening
A relatively rare form of griefing is called Flattening. Flattening happens when a griefer begins to completely level out a map, leaving it totally flat, desroying any structures along the way. Flattening is a rare practise because it takes a long time to accomplish and is usually only done while no Ops are on the server to stop them.

Hacks
Hacks are programs that manipulate Minecraft in a way that was not originally intended by Notch.
 * Flying - Now in widespread use by both griefers and normal players, this is a common and easy to obtain hack that can allow griefers to easily reach tall structures and begin deconstruction of areas that will be difficult to reach by players lacking this hack.
 * Auto-click - Another common tool of a griefer is the auto-click program. This automatically causes the mouse to click much faster than can normally be done by hand, which allows the player to quickly and messily place or delete blocks.
 * Noclip - Noclip allows players to go through solid blocks. This can be used to escape Spawn Jails. However, some servers have noclip quards in their MOTD which only lets Ops use the feature. Still, a griefer can obtain a noclip hack which lets them bypass the MOTD.

Social Engineering
Social Engineering is when a griefer manipulates players into thinking that they are decent and trustworthy players, as well as directing the blame of griefing to someone else. This sort of griefer is significantly more dangerous than others due to their ability to blend in with innocent and trusted players. This can cause confusion throughout the server and can even cause un-deserved bans on other players. If the griefer is very dedicated to a server, they may even become an Op. When this happens, they can use their power to deop all other ops and ban them, and can then grief as much as they please without anyone to stop them. If this worst case scenario occurs, the Admin can use operator commands through the server's console to deop the griefer and reop themselves.

Time
Some griefers will wait in a server, pretending to be away, or return to it when there are no ops online, at which point they could destroy as much as they please until another admin logs in.

Bots
Bots are very uncommon and sometimes attack in swarms. Not much is known about exactly how they work or their full capabilities, but bots are very dangerous and are generally only employed if a specific server has been "targeted". Bots are programs that take control of an account they've logged into and can act very human-like. It is suspected that if an Op is getting suspicious toward the bot, the hacker can speak for the bots when they are questioned. Bots come complete with many automatic actions that can instantaneously create pyramids or massive holes in any structure; they also fly around and employ random destruction griefing. IP banning and kicking are useless as the bots can switch IPs and account names in seconds and come right back. The only real defense is to shut down the server and wait until they don't come back.

Some of the behaviors bots have been seen to exhibit are:
 * Not speaking unless spoken too, such as not asking to be let out of a Spawn Jail.
 * Using long, misleading names that are difficult to type. To attack this, usernames can be automatically typed by opening the tab menu and clicking the username of choice.
 * Frequent jumping (although this is exhibited by many human players as well)
 * No clear purpose or destination, they wander (Many human players do this as well, to explore the server's existing creations)

Griefer swarms
While one griefer can be bad, on occasions they may attack in groups. Sometimes member of the swarm blaming other griefers in the group to avoid being caught. They can also attack rapidly, typically abusing vote bans to clear out the server if vote bans exist on the server. A typical sign is about four people (four is a common vote ban threshold) people joining at once, but that can be coincidence.

The swarm also provides the problem of taking longer to ban, although the server can be shut down to quickly stop any griefing.