This is the username used by the maintenance script rebuildMessages.php. The script is part of MediaWiki, it updates MediaWiki interface messages to be equal to the MediaWiki default. It is not a bot and cannot be blocked.
The script has two modes of operation:
- rebuildMessages.php --update
- Updates any messages which were last edited by "MediaWiki default" to their current version. Creates any messages which did not exist.
- rebuildMessages.php --rebuild
- Updates all messages to their current default value, regardless of whether they have been manually edited. This is sometimes used on other wikis when a new messages file has just been created, with a comprehensive set of default messages. It has never been used on the English Wikipedia.
Older edits made by this script had a user ID of zero, so they are treated as anonymous edits in the page history, with a link to the user contributions instead of the user page. Newer edits have a nonzero user ID.
The same username is also used by the MediaWiki installer. Installing MediaWiki has the same effect as rebuildMessages.php --update.
If there is a problem with the text of the default messages, please file a bug report at http://bugzilla.wikimedia.org/. Requests to start or stop the script should be made to the #wikimedia-tech channel on irc.freenode.net.