During Disemba 2005, about 27,000 users made at least five edits to Wikipedia; of these, 17,000 worked on the English edition. Maintenance tasks are performed by a group of volunteers; these include developers, who work on the MediaWiki software, and other trusted users with various permission levels including ""steward"", ""bureaucrat"" and ""administrator"". Stewards and bureaucrats are able to promote or demote users to different permission levels. Administrators are the largest group of specially privileged users, and have the ability to delete pages, prevent articles from being edited, or block users from editing. Administrators are, however, required to follow community policy when exercising these powers. These permissions are normally granted by community consensus; stewards are elected at irregular intervals. Vandalism or the minor infraction of policies may result in a warning or temporary block, while long-term or permanent blocks for prolonged and serious infractions are given by<citation need> (or in the name of) Jimmy Wales or, on the English-language edition, an elected ""Arbitration Committee"".