Vandalism is the conspicuous defacement or destruction of a structure, a symbol, or information against the will of the owner/governing entity. In the context of an online community project, it is a usually deliberate attempt to damage the usefulness of content for other viewers.
Assuming good faith
Useful community content presents the widest range of relevant and accurate information on a topic. In the case of a wiki, if someone edits a page so it reflects only a single viewpoint, that can be considered vandalism. For example, if a page about a TV show character contains information both from the show itself and from spin-off shows, books, etc., and a user removes all information that isn't strictly from the main show, the other community members will likely see that as vandalism. However, to keep good faith, you might assume that this editor was only trying to show that any source of information on that character besides the main show isn't true canon and shouldn't be in the article.
In general, an edit that seems like deliberate vandalism is often just a clumsy attempt at editing by someone who is new to wikis, simply didn't know the community's rules, or someone who didn't know how else to propose a change in how things are done on the wiki. In those cases, you can explain to that bad editor what they could do better, where they could go to discuss their ideas, and why certain things are just not allowed on your community, even if they're okay elsewhere. That way, a user who first seems like a vandal can turn into a useful editor and member of the community. Unless you can clearly see that someone had bad intentions, always assume they just didn't know better and offer your help!
Avoiding critical mass
Vandalism is often an aggressive attempt at getting a point across to the community, by an angry or spiteful user. You can try to defuse the situation by talking to the vandal, suggesting to work things out peacefully, or by explaining better ways to achieve what the vandal wants to achieve. If you alienate the editor, however - for example by insulting them right back - vandalism can turn into a form of vengeance. Fandom has tools and mechanisms in place to minimize the effect of pranksters and can even handle a few determined vengeful vandals, but dealing with a full-blown vandalism movement is much harder and costs a lot of time and effort.
Because of this, you should assume good faith and react with kindness wherever possible to avoid making the vandal(s) even more hateful and to prevent a vandal attack from reaching critical mass.
Dealing with vandalism
In general, the best way to deal with vandalism is to revert the vandalism, block the vandal, and ignore any attempt from the vandal to bother you further. For more information on this, we recommend reading these three pages, which go into each of these steps in more detail:
There are measures administrators can put in place to help prevent vandalism before it begins:
Two anti-vandalism extensions are used often on Fandom. ProtectSite locks down the ability of specific user groups from being able to do basic actions, such as editing or creating pages or uploading images, for up to 12 hours. If a community is facing a surge of vandalism, the SOAP or Fandom Staff can enable ProtectSite to prevent new, unregistered, or even non-sysop users from being able to do those particular things. The other extension is AbuseFilter, which allows skilled coders to block the submission of edits if certain conditions are met, for example if a particular rude or inappropriate word is included in the new text. SOAP can help a community set up filters against regular vandalism.
Admins and Fandom staff can also turn off anonymous editing in wiki features if anonymous accounts (identified by their IP address) continually cause problems on a community.