AbuseFilter is a MediaWiki extension used to prevent vandalism and spam. Administrators and other privileged users create filters that analyze actions to the wiki (such as making an edit or creating an account) and detect specific likely abusive behavior patterns (for example, edits that introduce only repeated letters). AbuseFilter managers can mark individual filters as public or private. Public filters allow any user to view the filter's source code and the log of its related hits (times when the filter was activated). Private filters (source code and hits) are restricted to AbuseFilter managers.
AbuseFilter filters can match edits, page moves, file uploads, account creations and more. AbuseFilter creators can choose among the following actions to be triggered when a matching edit is found: tag the edit, prevent the edit, warn the user with a custom interface message, or block the user. Whenever an edit trips the filter, it is logged. Full documentation for the AbuseFilter extension is available on MediaWiki.org.
The technical work to create a global (across a set of Wikimedia wikis) AbuseFilter started in 2009. In 2012, a proposal to create a Global AbuseFilter was created on Meta-Wiki. A vote was held on Meta-Wiki talk page, with a majority of supports, but the discussion was not well-advertised and had little participation. For almost two years, the proposal languished, but technical development slowly continued. In 2013, Global AbuseFilters were enabled on a limited set of wikis (metawiki, specieswiki, incubatorwiki, testwiki, test2wiki, mediawikiwiki, and in 2014 "small wikis"). This was the beginning of the trial phase. Global filters were recently enabled on "medium sized wikis" as well. Some rules about global filters were proposed, but never completely accepted. There is an ongoing request for comment on policy governing the use of the global AbuseFilters. In the meantime, specific wikis can opt out of using the global AbuseFilter. These wikis can simply add a request to Global AbuseFilter/Opt-out wikis.